Analyzing the Properties of Air-Covered Yarn Manufactured Knit Fabric

Analyzing the Properties of Air-Covered Yarn Manufactured Knit Fabric

Afroja Alam Anika, Dip Jyoti Das¹, Sanjana Islam & Md. Sajid Hossain
Department of Yarn Engineering
Bangladesh University of Textiles
Email: [email protected]¹

Abstract

This research investigates the mechanical and comfort-related properties of knitted fabrics manufactured from Air-Covered Yarns (ACY). With the global demand for high-performance stretch fabrics projected to reach USD 24.58 billion by 2032, a notable research gap exists in understanding how specific core–sheath yarn combinations influence the functional performance of the resulting fabrics. This study addresses that gap by systematically analyzing different ACY compositions, including Polyester–Viscose–Elastane and Cotton–Lyocell–Elastane yarn systems.

The experimental methodology evaluates the influence of ACY structural parameters on key fabric performance characteristics such as bursting strength, air permeability, GSM, and elastic recovery. Microscopic analysis revealed that fabrics containing elastane yarn exhibited tighter and more compact loops, while fabrics without elastane showed looser loops. Polyester filaments displayed smooth surfaces, whereas cotton–lyocell blends exhibited increased hairiness and bulk. Porous structures and micro-voids created by air-covered and elastic yarns enhanced breathability without significantly compromising mechanical strength.

The findings establish a clear relationship between yarn composition, fiber blend, and fabric performance, providing a technical basis for optimized yarn selection in the development of activewear, hosiery, and seamless knitted garments. This research offers practical insights for textile engineers and manufacturers aiming to enhance the durability, comfort, and functional performance of stretchable fabrics.

1. Introduction

The performance of textile fabrics is largely governed by the type of fibres and yarn structures used in their construction. With increasing demand for comfort, durability, and functional properties, the textile industry has diversified its use of natural, synthetic, and regenerated fibres. Yarn formation serves as a crucial link between fibres and fabric, directly affecting mechanical and comfort-related properties. Traditional yarn manufacturing methods have been continuously refined to improve fabric quality and production efficiency. Consequently, ongoing advancements in yarn technology play a vital role in meeting modern textile performance requirements.

1.1. Background of the Project

Textile materials have played a pivotal role in human civilization, evolving from natural plant and animal fibres to a wide range of synthetic and regenerated fibres over the centuries. Natural fibres such as cotton, wool, silk, and linen are renowned for their comfort, breathability, and biodegradability, while synthetic fibres like polyester, nylon, and viscose are valued for durability, elasticity, and resistance to moisture and wrinkling [1], [2]. The modern textile industry leverages both natural and synthetic fibres to create fabrics that meet complex functional and aesthetic requirements, ranging from apparel and home textiles to technical and medical textiles [3].

The transformation of fibres into yarn is at the very heart of fabric formation and significantly influences fabric performance, including strength, flexibility, dimensional stability, and comfort [4]. For a long time, traditional spinning methods such as ring spinning and rotor spinning have been the mainstay of yarn production, providing reliable mechanical properties. However, the growing demand for high-performance fabrics, stretchable garments, and more efficient production techniques has led to innovations in yarn manufacturing technology, including composite and covered yarns [5].

Covered yarns are a special type of composite yarn in which one or more filaments or spun yarns are wrapped around a core yarn. This configuration combines the elasticity or strength of the core with the functional and aesthetic properties of the sheath [6]. Traditional covering methods, while effective, often face limitations such as slower production speeds, uneven coverage, and reduced flexibility. To overcome these challenges, air covering technology was developed, utilizing compressed air to wrap the outer layer around the core at high speed.

Air-covered yarns (ACY) are an advanced type of composite yarn that typically use an elastic filament core, such as spandex, along with a polyester, nylon, or cotton sheath. High-velocity air entangles the sheath filaments around the core without mechanical twist, producing a yarn that is uniform, smooth, and highly stretchable [7]. This technology enables high-speed production while maintaining yarn quality, reducing hairiness, and ensuring consistent dimensional properties. ACY finds applications in stretchable tops, hosiery, sportswear, and seamless textiles, where elasticity, recovery, and comfort are critical [8].

The structural characteristics of air-covered yarns significantly influence fabric properties. Fabrics made from ACY exhibit enhanced stretchability, improved recovery, and better fit due to the elastic core and air-entangled sheath. Additionally, air pockets formed during production improve breathability and moisture management, making ACY fabrics suitable for activewear and performance textiles. These yarns also offer manufacturing advantages, as the air covering process reduces mechanical steps and energy consumption compared to traditional covering methods [9]. The global stretch fabric market has experienced significant growth due to increasing demand for comfort, flexibility, and performance in apparel and activewear. In 2025, the worldwide stretch fabric market was valued at approximately USD 14.5 billion and is projected to reach USD 24.58 billion by 2032, growing at a compound annual growth rate (CAGR) of 6.45% [10].

1.2. Research Gap of the Project

Despite the increasing industrial significance of air-covered yarns (ACY) in stretchable fabrics, there remain critical gaps in understanding the influence of different core and sheath yarn combinations on the final fabric properties. Most previous studies have primarily focused on the production technology, surface smoothness, and mechanical characteristics of ACY, such as hairiness, tensile strength, and dimensional stability [6], [7]. While these studies demonstrate the general benefits of ACY, there is limited systematic research on how varying ratios and types of core and covering yarns affect fabric performance parameters such as stretchability, recovery, moisture management, and comfort.

Furthermore, although composite yarns with elastic cores like spandex have been extensively studied, the effect of alternative core-sheath combinations involving polyester, cotton, or viscose in high-performance stretch fabrics has not been fully explored [8]. Existing literature largely addresses ACY applications in hosiery and sportswear but provides minimal guidance for optimizing yarn selection for specific functional requirements. Additionally, the interaction between yarn structure and fabric-level properties under real-world loading and wearing conditions remains inadequately investigated [9]. Addressing these gaps is crucial for improving fabric design and expanding the applications of air-covered yarns in modern textile engineering. A systematic study examining various yarn combinations will provide essential insights for manufacturers and designers to optimize stretch fabrics for both performance and comfort.

1.3. Objectives of the Project

The primary objective of this study is to evaluate how different yarn combinations affect the properties of fabrics made from air-covered yarns (ACY). Specifically, the research aims to:

1. Investigate the influence of various yarn combinations (e.g., polyester-viscose, cotton-lyocell-elastane) on the mechanical properties of ACY fabrics, including bursting strength and abrasion resistance [4], [5].
2. Examine the effect of ACY structure on fabric comfort properties such as air permeability and moisture management [3], [4].
3. Compare the performance of ACY fabrics against conventional fabrics to assess potential improvements in functional and aesthetic properties [7], [8].
4. Provide insights for designers, engineers, and manufacturers on selecting optimal yarn combinations for high-performance and stretchable textiles [8], [9].

By achieving these objectives, this study seeks to bridge the existing research gap regarding the systematic evaluation of ACY fabrics with different yarn combinations, thereby aiding the development of functional, durable, and comfortable stretchable textiles for apparel, sportswear, and home textile applications.

1.4. Significance of the Project

The study of air-covered yarn (ACY) fabrics using different core and sheath yarn combinations is significant for advancing both textile technology and industrial applications. ACY fabrics provide superior elasticity, recovery, dimensional stability, and fabric surface uniformity, which are essential for high-performance textiles, including sportswear, activewear, hosiery, and seamless garments [7], [8]. By understanding the relationship between core and covering yarns, manufacturers can optimize fabric performance, improve material efficiency, and reduce waste during production [5], [6].

The growing global demand for stretchable and performance textiles underscores the importance of this study. Consumer expectations for comfort, flexibility, breathability, moisture management, and durability are steadily increasing, driving the need for fabrics with precisely engineered yarn structures [10]. ACY allows high-speed production without compromising quality, making it cost-effective and suitable for large-scale manufacturing [7], [9]. From a research and innovation perspective, studying ACY with varied yarn combinations can provide insights into how fiber type, yarn tension, and sheath arrangement affect mechanical and functional properties such as tensile strength, elongation, air permeability, and pilling resistance [6], [7]. These insights can inform the design of new fabric types tailored for specific applications, such as performance sportswear, compression garments, and stretchable technical textiles [8]. Additionally, integrating sustainable or recycled fibers into ACY fabrics aligns with environmental objectives. The reduction of mechanical processing steps in air covering technology lowers energy consumption, and using blends of natural, synthetic, and recycled fibers contributes to eco-friendly textile production [9], [10]. Therefore, this study provides value by combining practical, industrial, and environmental considerations, supporting innovations that enhance fabric functionality, quality, and sustainability in modern textile manufacturing.

2. Literature Review

The performance of knitted fabrics is influenced by the combined effects of fiber characteristics, yarn properties, and fabric structure. Knitted fabrics differ fundamentally from woven fabrics due to their looped construction, which provides superior extensibility, flexibility, and comfort, while also increasing sensitivity to yarn parameters. Previous studies have reported that fiber properties such as tensile strength, elongation, moisture regain, surface morphology, and elastic recovery play a critical role in determining yarn behavior during spinning and knitting. Additionally, yarn characteristics including linear density, twist, strength, hairiness, and structural configuration significantly affect key fabric properties such as density, air permeability, bursting strength, pilling resistance, and elongation. Recent research on modern stretch and performance textiles emphasizes the importance of understanding the interrelationship between fibers, yarn structure, and knitted fabric performance.

2.1. Introduction

The performance of knitted fabric depends on the combined effect of fibers, yarn, and fabric construction. Knitted fabric differs from woven fabric in the sense that knitted fabric contains a series of interconnected loops, which provide extensibility, flexibility, and comfort to the fabric, but at the same time make it sensitive to yarn effects [11]. Fiber properties such as tensile strength, elongation, moisture regain, surface characteristics, and elastic recovery affect yarn properties during yarn manufacturing and fabric knitting [12]. Yarn properties such as linear density, twist, strength, hairiness, and core and sheath effects affect fabric density, air permeability, bursting strength, pilling, and elongation [13].

In modern textile materials such as activewear and stretch materials, composite yarns have become popular materials. Air-covered yarn (ACY) technology combines elastane and staple or filament yarns in an efficient manner, and knitted fabrics have optimal comfort and dimensional stability [14]. Thus, a comprehensive knowledge of fibers, yarn, and yarn structure is required to understand air-covered yarn manufactured fabrics.

2.2. Natural Fibers Used in Spinning for Knitted Fabrics

Natural fibers are derived from plant and animal sources and are valued for their comfort, breathability and biodegradability. In spinning applications, natural fibers are widely used either alone or in blends with regenerated and synthetic fibers to balance comfort and durability [15].

2.2.1. Cotton Fiber

Cotton is the most widely used natural staple fiber, obtained from the seed hair (trichomes) of Gossypium species. It is the most extensively used natural fiber in the textile industry, accounting for approximately 33% of global fiber consumption [16]. Cotton is extensively used in spinning, weaving, and knitted fabric production due to its comfort, breathability, moisture absorbency, and versatility.

It has a single elongated cell structure composed of three main components: cuticle, primary/secondary cell walls, and lumen. The cuticle forms the outermost layer, consisting of waxes and pectic substances that protect the fiber and influence fiber-fiber friction during spinning, which affects yarn cohesion and processing performance [17]. The primary and secondary walls form the main body of the fiber. The primary wall is thin and flexible, while the secondary wall consists of concentric layers of cellulose fibrils arranged helically, providing strength, stiffness, and flexibility to the fiber. The lumen, a hollow central core, collapses upon drying, producing the ribbon-like convolutions characteristic of cotton fibers, which enhance spinnability and yarn cohesion [18].

Chemical Composition of Cotton Fiber
The chemical composition of mature cotton fiber is dominated by cellulose, which governs its physical behavior, moisture regain, and mechanical strength. Minor non-cellulosic components influence fiber flexibility, surface characteristics, and processing behavior.

Table 1. Chemical Composition of Cotton Fiber

Physical and Mechanical Properties of Cotton Fiber
The suitability of cotton for yarn formation and fabric manufacturing depends on its physical and mechanical properties, which are commonly evaluated using standard fiber testing methods, including High Volume Instrument (HVI) analysis. These properties directly affect spinnability, yarn strength, uniformity, and fabric comfort [19].

Table 2. Physical and Mechanical Properties of Cotton Fiber

2.2.2. Wool Fiber

Wool is a natural protein-based animal fiber obtained primarily from sheep. It has a complex multicellular structure composed of three main components: cuticle, cortex, and medulla. The cuticle consists of overlapping scale-like cells oriented toward the fiber tip, which create a directional friction effect, responsible for wool’s characteristic felting behavior under moisture, heat, and mechanical action [20]. The cortex forms the main body of the fiber, and in fine wool is bilateral, consisting of ortho-cortex and para-cortex, which differ in chemical reactivity and swelling behavior. This arrangement produces the fiber’s natural three-dimensional crimp, contributing to bulk, elasticity, and thermal insulation. The medulla, a hollow or porous core, is usually present in coarse fibers and enhances fiber bulk and insulation while reducing uniformity [21].

Chemical Composition Wool Fiber
Wool is composed primarily of keratin protein, which contains approximately 20 amino acids. A notable feature of wool keratin is its high sulfur content (~3–4%), largely in the form of cystine disulfide bonds, providing structural stability, resilience, and elasticity. At the molecular level, wool keratin exists mainly in α-helix (α-keratin) conformation, which can unfold into β-sheet (β-keratin) when stretched, allowing high extensibility and recovery [22].

Table 3. Chemical Composition of Wool Fiber

Physical and Mechanical Properties

Table 4. Physical and Mechanical Properties of Wool Fiber

2.2.3. Silk Fiber

Silk is a natural protein-based fiber produced by insects and spiders. It is unique among natural fibers for being produced as a continuous filament, which gives it a smooth surface, high lustre, and exceptional tensile strength [23]. Silk is extensively used in high-quality yarns and fabrics due to its strength, extensibility, and aesthetic appeal.

Silk fibers are primarily classified into cultivated silk (Bombyx mori), produced by the mulberry silkworm, and wild and spider silks, which include multiple types such as dragline silk (Nephila), each with specific mechanical properties.

Chemical Composition
The main protein in silk is fibroin, forming the primary structural component. In cultivated silk, fibroin filaments are bound by sericin, a gummy protein typically removed during degumming to reveal the lustrous fiber. Silk fibers have a hierarchical structure with β-pleated sheets, providing high strength and stability. Bombyx mori silk has a higher crystalline content (~70–80%) than most spider silks, while amorphous regions contribute to elasticity and softness [24].

Table 5.Chemical Composition of Silk Fiber

 Physical and Mechanical Properties

Silk fibers are known for high tensile strength, extensibility, lustre, and visco elastic properties.

Table 6.Physical and Mechanical Properties of Silk Fiber

2.3. Synthetic and Regenerated Fibers Used in Spinning for Knitted Fabrics

Synthetic and regenerated fibers are widely used in spinning for knitted fabrics due to their consistent quality, high strength, durability, and controlled functional properties [25]. Unlike natural fibers, synthetic fibers are produced through chemical polymerization, while regenerated fibers are derived from natural polymers (mainly cellulose) that are chemically processed and re-formed into fibers.In knitting applications, these fibers are commonly used alone or in blends with natural fibers to improve dimensional stability, wrinkle resistance, elasticity, abrasion resistance, and production efficiency, while maintaining acceptable comfort levels. The most important synthetic and regenerated fibers used in spun yarns for knitted fabrics include polyester, nylon (polyamide), acrylic, viscose (including eco-viscose), modal, and lyocell.

2.3.1. Polyester

Polyester, chemically known as Polyethylene Terephthalate (PET), is the most widely produced synthetic fiber worldwide. Its extensive use in the textile industry is attributed to its low cost, high durability, dimensional stability, and versatility [26]. Polyester fibers are commonly used in apparel, home textiles, industrial fabrics, and technical applications.

PET is a thermoplastic, hydrophobic fiber produced primarily by melt spinning and is available in both continuous filament and staple fiber forms, allowing its use in woven, knitted, and nonwoven structures.

Production and Strategic Importance
The widespread adoption of polyester fibers is driven by several key factors:

• Availability: Polyester provides a consistent and scalable alternative to natural fibers, whose supply may fluctuate due to climatic and agricultural limitations.
• Engineering Control: Fiber properties such as fineness, strength, cross-sectional shape, and crimp can be precisely controlled during polymerization, spinning, and drawing processes [27].
• Blending Capability: Due to its low moisture regain and tendency to generate static electricity, polyester is frequently blended with natural fibers to enhance durability, crease resistance, and service life of textile products.

Physical and Mechanical Properties
Polyester is characterized by high tensile strength, high modulus, and excellent resilience. Its resistance to abrasion and deformation makes it suitable for applications requiring long-term performance and shape retention.

Table 7.Physical and Mechanical Properties of Polyester (PET)

Thermal Properties
Polyester is a thermoplastic fiber, which softens and melts upon heating. This property allows fabrics to be heat-set, providing permanent pleats, improved crease recovery, and dimensional stability [28].

• Glass transition temperature (Tg): ~70 °C
• Softening temperature: 230–245 °C
• Melting temperature: 250–268 °C
• Recommended ironing temperature: ~135 °C
• Nylon (Polyamide Fiber)

2.3.2. Nylon (Polyamide Fiber)

Nylon is the first fully synthetic fiber commercially produced. It belongs to the polyamide family and is a thermoplastic fiber characterized by repeating amide groups(–NH–CO–) along its polymer chain [29]. It is widely used in hosiery, swimwear, sportswear, carpets, ropes, tire cords, and blended yarns because of its high strength, elasticity, abrasion resistance, and durability.

The two main nylon types used in textiles are:

• Nylon 6,6 – produced from hexamethylenediamine and adipic acid.
• Nylon 6 – produced from caprolactam.

Nylon fibers are produced by melt spinning followed by drawing, which aligns the molecular chains along the fiber axis and increases crystallinity, resulting in high strength and toughness. Morphologically, fibers are smooth, uniform, and glass-like, typically circular in cross-section. Trilobal or multilobal cross-sections may be engineered to improve lustre, bulk, and soil-hiding properties [30].

Physical & Mechanical Properties
Nylon is highly valued for its toughness, elasticity, abrasion resistance, and resilience, making it suitable for high-performance textiles.

Table 8. Physical & Mechanical Properties of Nylon (6 and 6,6)

Thermal Properties
Nylon is a thermoplastic fiber, which allows heat-setting to improve dimensional stability, crease recovery, and fabric performance.

• Melting temperature (°C) of Nylon 6: 215–225& Nylon 6,6: 250–260

2.3.3. Acrylic

Acrylic fibers are synthetic fibers composed of at least 85% acrylonitrile units. They were developed as a lightweight alternative to wool, offering high bulk, soft handle, excellent thermal retention, and easy-care properties [31]. Acrylic is widely used in sweaters, blankets, hand-knitting yarns, cotton blends, and outdoor textiles due to its softness, warmth, and durability. Many acrylic fibers are bicomponent, producing a permanent, reversible spiral crimp that mimics the natural crimp of wool.

Acrylic is typically produced by wet spinning or dry spinning. Its cross-sectional shapes, such as dog-bone or bean shapes, contribute to fiber bulk, stiffness, and thermal insulation.

Physical & Mechanical Properties
Acrylic fibers are low density and lightweight, with high extensibility and good elastic recovery, making them suitable for knitted fabrics and blended yarns.

Table 9. Physical & Mechanical Properties of Acrylic Fiber

Thermal Properties
Acrylic fibers are thermoplastic and provide excellent thermal insulation due to their bulky structure, which traps air. They soften at 190–230°C and decompose before melting.

2.3.4. Lycra (Elastane/Spandex)

Lycra is the brand name for elastane (spandex in North America), a manufactured fiber composed of at least 85% segmented polyurethane. The polymer chain features alternating “soft” segments, which provide high elasticity, and “hard” segments that act as cross-links, ensuring strength and the ability to return to the original length after stretching [33].

Physical and Mechanical Properties
Lycra is an elastomeric fiber, notable for its exceptional stretch and recovery. It can elongate up to 500–800% of its original length without rupture and exhibits nearly 100% elastic recovery. While its tenacity is relatively low (approximately 0.6–0.9 cN/dtex), this is adequate for its primary function, which is providing elasticity rather than structural strength. The fiber has a density of approximately 1.20–1.25 g/cm³, contributing minimally to fabric weight while enabling high stretch performance [34].

Thermal Properties
Lycra is thermoplastic, softening at 175–190°C and melting around 230–250°C. Its thermal behavior allows it to be incorporated into composite yarns without loss of performance. It maintains dimensional stability under moderate heat, but prolonged exposure to high temperatures can degrade the fiber.

2.3.5. Regenerated Cellulosic Fibers

Regenerated cellulosic fibers are man-made fibers derived from natural cellulose, designed to combine the comfort of natural fibers with versatile processing properties [35].

The most common types include:

• Viscose: The oldest commercial regenerated fiber, developed to imitate the lustre and drape of silk at lower cost.
• EcoVero Viscose: A sustainable variant of viscose, sourced from certified forests, with lower emissions and water impact.
• Modal: A High Wet Modulus (HWM) viscose with improved wet strength, softness, and dimensional stability.
• Lyocell (Tencel™): The latest generation, produced via a closed-loop solvent process, highly eco-friendly and strong, with excellent moisture management.

These fibers are primarily used in apparel, intimate wear, home textiles, towels, and high-end fashion, offering soft handle, drape, and thermal comfort.

Physical & Mechanical Properties
Regenerated cellulosic fibers have varying tenacity, cross-sectional shapes, moisture regain, and wet/dry strength ratios, which influence their suitability for different textile applications [36].

Table 10.Physical & Mechanical Properties of Regenerated Cellulosic Fibers

Thermal Properties
These fibers are thermoplastic, allowing moderate heat-setting during fabric finishing. They provide good thermal comfort due to moisture absorbency and air-trapping bulk.

Table 11.Thermal Properties of Regenerated Cellulosic Fibers

2.4. Yarns Used in Knitted Fabrics

Yarns are continuous strands formed from fibers or filaments that are systematically arranged and twisted to develop strength and cohesion suitable for textile production. In knitted fabrics, the properties of the yarn directly influence fabric performance, including mechanical behavior, comfort, dimensional stability, surface appearance, and hand feel [37]. Yarn characteristics such as fiber type, twist level, structural uniformity, and hairiness play a significant role in determining the stretch, resilience, abrasion resistance, and aesthetics of knitted textiles.

Knitted fabrics predominantly use spun yarns and composite yarns, which may be produced from natural, synthetic, or regenerated fibers either alone or in blends to balance comfort and performance. The principal types of yarns used in knitted fabric production include ring‑spun, rotor‑spun, air‑jet spun, core‑spun (covered) yarns, and novelty/fancy yarns, each imparting distinct structural and functional attributes to the resulting knit [38].

2.4.1. Classification by Fiber Composition and Continuity

Spun (Staple) Yarns:
Composed of short, discrete fibers such as cotton, wool, or cut synthetic staples. Twist is applied to bind the fibers into a cohesive strand. The yarn surface exhibits protruding fiber ends, resulting in a “fuzzy” texture that improves thermal insulation and provides a soft, matte hand-feel.

Filament Yarns:
Constructed from continuous fibers of essentially infinite length, such as natural silk or synthetic polymers like polyester and nylon. Filament yarns are smoother and more lustrous than staple yarns. They may exist as single strands (monofilament) for high durability or bundled filaments (multifilament) for enhanced flexibility and softness.

Textured Yarns:
Filament yarns can undergo mechanical and thermal texturizing, such as draw-texturing or false-twist texturing, to introduce crimps, loops, or bulk. This process improves elasticity, hand-feel, and thermal properties, making smooth filaments mimic the characteristics of natural staple yarns.

2.4.2. Classification by Yarn Structure

Simple Yarns:
The fundamental yarn unit is the single yarn, produced by a single twisting operation. Ply or folded yarns are created by twisting two or more single yarns together to improve strength, uniformity, and stability. Multiple ply yarns can be further twisted to form cords or ropes for heavy-duty applications.

Fancy (Novelty) Yarns:
Designed for decorative or functional irregularities, fancy yarns include:

• Slub Yarn: Exhibits alternating thick and thin sections along the length.
• Loop/Bouclé Yarn: Contains small loops at regular intervals for textured surfaces.
• Chenille Yarn: Features a soft, caterpillar-like pile, providing a plush appearance and feel.

Composite and Core-Spun Yarns:
These yarns combine different fibers to achieve specific performance characteristics. A common example is core-spun yarn, where an elastic filament (such as spandex) forms the central core wrapped with staple fibers, combining stretch, recovery, and natural fiber hand-feel.

2.4.3. Classification by Processing Technology

Ring-Spun Yarns:
Traditional method producing yarns with dense helical fiber arrangement. Fibers migrate between core and surface, resulting in strong, fine yarns suitable for high-quality apparel [39].

Rotor (Open-End) Spun Yarns:
Produced by depositing fibers into a rotating rotor. The yarn has a disordered core with surface “wrapper fibers.” These yarns are bulkier, more absorbent, and pilling-resistant but generally weaker than ring-spun yarns.

Air-Jet Yarns:
Continuous filaments or staple fibers are wrapped around a core using high-pressure air streams. Air-jet yarns have minimal hairiness, reducing friction and fiber shedding, making them ideal for high-speed industrial knitting.

Vortex Yarns:
Similar to air-jet technology, vortex spinning uses a high-speed airflow to impart twist on fibers around a core. This process produces yarns with a smooth surface, moderate bulk, and high strength. Vortex yarns are often used in knitted fabrics where low hairiness, abrasion resistance, and uniform appearance are required.

2.5. Air Covered Yarn

Air-Covered Yarn (ACY) is a high-performance yarn produced by combining a core filament, typically Spandex/Elastane, with a covering yarn such as Nylon or Polyester or Cotton or Cotton blend. Unlike traditional mechanically-covered yarns, ACY employs high-pressure compressed air to interlace the covering filament around the core at rhythmic intervals, creating periodic entanglement points rather than a continuous spiral wrap [40].

2.5.1. Production Process

ACY production is highly efficient due to the air-jet intermingling technique:

• One-Step Feeding: Both the core filament and covering yarn are simultaneously fed into a specialized air-jet nozzle.
• Fiber Intermingling: High-pressure air streams swirl the covering filaments around the core, forming discrete “tack points” that maintain fiber alignment and stability.
• Resulting Structure: The yarn exhibits a parallel arrangement with intermittent entanglement rather than a helical spiral, ensuring elasticity, resilience, and a softer hand feel.

2.5.2. Physical and Mechanical Properties

ACY is designed for high elasticity and dimensional stability:

Table 12.Physical and Mechanical Properties of ACY

 Comparison with Mechanically Covered Yarn (SCY)

3. Materials & Methods

This study was conducted to examine the effect of yarn composition on the properties of knitted fabrics. Five air-covered yarn samples with different material combinations were selected as the experimental materials. All yarns were produced using the same air-covering technique to ensure uniform processing conditions. The yarns were then converted into single jersey knitted fabrics under identical manufacturing parameters. The produced fabrics were evaluated to assess the influence of material variation on fabric performance.

3.1. Materials

Five air-covered yarn samples with different fiber compositions were selected for this study. The yarns included natural, regenerated, synthetic, and elastomeric fibers in various combinations. All raw materials were procured from verified suppliers to ensure quality and consistency. Yarns were coded as Sample A, B, C, D, and E for systematic evaluation. These materials served as the basis for fabric production and subsequent property analysis.

3.1.1. Yarn Materials & Sample Composition

In this research work, five different air- covered yarn samples were used to investigate the influence of yarn composition on selected fabric properties. All yarn samples were produced using air covering technique; however, the composition of the yarns was varied among the samples. The samples were coded as sample A, sample B, sample C, sample D and sample E for convenience and systematic analysis.

Sample A:
Composition: 48 S/3: 42S Eco Vero Viscose (white)+75D White Polyester (36F)

Raw Materials:

• Eco Vero Viscose
• Polyester

Fibre types:

• Regenerated cellulosic fibre (Eco Vero Viscose)
• Synthetic fibre (Polyester filament)

Sample B:
Composition: 46 S/3: 40S Eco Vero Viscose (white)+40S Eco Vero Viscose (white)+ 75D Black Polyester (36F)

Raw Materials:

• Eco Vero Viscose
• Polyester

Fibre types:

• Regenerated cellulosic fibre (Eco Vero Viscose)
• Synthetic fibre (Polyester filament)

Sample C:
Composition: 93 S/2: 75 Black Polyester (36F) +40D Lycra

Raw Materials:

• Lycra
• Polyester

Fibre types:

• Elastomeric synthetic fibre
• Synthetic fibre (Polyester filament)

Sample D:
Composition: 74 S/2: Recycled White Polyester (36F)+70D Lycra

Raw Materials:

• Lycra
• Polyester

Fibre types:

• Synthetic fibre (Polyester filament)
• Elastomeric synthetic fibre

Sample E:
Composition: 57S/3:40S1 Cotton + Lyocell (60+40) mélange Rose+75D Recycled Polyester (36F) +70D Lycra.

Raw Materials:

• Lyocell
• Polyester
• Cotton
• Lycra

Fibre types:

• Synthetic fibre (Polyester filament)
• Elastomeric synthetic fibre
• Natural fibre
• Regenerated cellulosic fibre

3.2. Yarn Manufacturing Method

We have manufactured all of our five yarn samples in the Sincro Multipla Air jet 410 Machine, manufacturer FADIS S.P.A.

3.2.1. Air Covering Machine and Process description

The air covering process was carried out based on the principle of pneumatic interlacing. We will observe the process parameters for Sincro Multipla Air jet 410 Machine, manufacturer FADIS S.P.A.

Process Parameters

• Air pressure: 6-8 bar
• Winding tension: 10-27%
• Overfeed%: 8-25%

Process Description
Initially, the core yarn was supplied from the creel and drafted to a predetermined draft ratio using the drafting unit. The stretched core yarn was then fed into the air jet nozzle. Simultaneously, the covering yarn was guided into the same nozzle through a separate feed system. High-pressure compressed air introduced into the nozzle generated a turbulent airflow, which caused the covering yarn to interlace and wrap around the core yarn in a random but uniform manner. No mechanical twisting was applied during this process; instead, yarn cohesion was achieved through air-induced interlacing. After interlacing, the air covered yarn was collected through the take-up system and wound into packages at a constant delivery speed.

Process Flow of Air Covering Machine

Yarn Supply (Creel Section)

↓

Tension Control

↓

Elastane Drafting

↓

Filament Overfeed

↓

Air Jet Covering

↓

Composite Yarn Formation

↓

Winding

↓

Package Formation

3.2.2. Fabric Manufacturing Method

Each air-covered yarn sample was converted into fabric form to evaluate its performance characteristics. The fabrics were produced at Lab Knitter Machine, Mesdan. Accordingly, five fabric samples corresponding to Sample A to Sample E were produced under identical manufacturing conditions. All fabric production parameters were kept constant to ensure that differences in fabric properties were primarily due to variations in yarn composition. Only the gauge was change according to the count of the yarn.

Fabric specifications:

• Fabric structure: Plain
• Knit type: Single jersey
• Fabric width:6.1-15.2 cm

4. Experimental Procedure

The experimental procedures were designed to evaluate the fundamental physical and performance characteristics of fabrics produced from air-covered yarns. All tests were conducted under controlled laboratory conditions to ensure accuracy and repeatability of results. Prior to testing, the fabric samples were properly conditioned according to standard atmospheric conditions. Each experiment was performed following relevant international testing standards, and multiple readings were taken for each sample to obtain reliable average values.

4.1. Conditioning of Samples

Prior to testing, all fabric samples were conditioned according to standard textile testing conditions. The samples were placed in a standard atmosphere of 20 ± 2°C temperature and 65 ± 2% relative humidity for at least 24 hours to achieve moisture equilibrium and ensure reliable test results.

4.2. Testing Standards

All tests were conducted according to relevant testing standards. Here is the table for testing methods & standards.

Table 13. Testing Methods & Standards

4.3. Testing Instruments

All experimental tests were conducted using calibrated and standard laboratory testing instruments to ensure accuracy and reliability of the measured data. The instruments were selected based on the specific testing requirements and relevant international standards. Details of the testing instruments used in this study are summarized in Table.

Table 14. Testing Methods & Instruments

4.4. Testing Methods

Five fabric samples were selected for experimental evaluation. Each sample was subjected to the same set of tests, namely fabric weight (GSM), air permeability, and bursting strength. For each test, multiple readings were taken from different areas of the fabric sample, and the average value was considered as the representative result for analysis. Some samples couldn’t be tested due to some fabric width limitation.

4.4.1. Air Permeability Test

The air permeability of the fabric samples was measured according to ASTM D737 standard method. Prior to testing, all fabric specimens were conditioned under standard atmospheric conditions of 65 ± 2% relative humidity and 21 ± 1°C temperature for at least 24 hours. The test was carried out using an air permeability tester with a fixed test area. Each fabric specimen was mounted securely on the test head, ensuring no air leakage around the edges. A constant pressure difference was applied across the fabric, and the rate of airflow passing perpendicular to the fabric surface was measured. The air permeability values were recorded in cm³/cm²/s. For each sample, measurements were taken at multiple locations, and the average value was reported as the final air permeability.

4.4.2. Bursting Strength Test

The bursting strength of the fabric samples was determined according to ISO 13938-2 standard (Pneumatic method). Prior to testing, all specimens were conditioned under standard atmospheric conditions of 65 ± 2% relative humidity and 21 ± 1°C temperature for at least 24 hours. Circular fabric specimens were clamped firmly over a rubber diaphragm of the bursting strength tester to prevent slippage or air leakage. Compressed air was applied at a constant rate, causing the diaphragm and fabric to expand uniformly until rupture occurred. The pressure at which the fabric burst was recorded as the bursting strength. The bursting test values were recorded in kpa. For each fabric sample, multiple tests were conducted at different locations, and the average bursting strength value was reported.

4.4.3. Fabric Weight (GSM)

The fabric weight per unit area (GSM) was measured using a simplified gravimetric method due to limited sample size. Fabric specimens of 1 inch × 1 inch (2.54 cm × 2.54 cm) were cut from each sample. Each specimen was weighed using an analytical balance with a precision of ±0.001 g. The GSM was calculated by dividing the weight of the specimen by its area converted to square meters.

5 specimens were measured for each fabric, and the average GSM was reported. It is noted that this method is a non-standard, approximate measurement intended to provide comparative fabric weights within this study.

4.4.4. Single Yarn Tensile Strength and Elongation at Break Test

Prior to testing, yarn samples were conditioned under standard atmospheric conditionsfor at least 24 hours. Individual yarn specimens were carefully mounted between the upper and lower clamps of the Autodyn 300 tensile tester. A constant rate of extension was applied until yarn rupture occurred. The maximum breaking force and elongation at break were automatically recorded by the machine software. The yarn tensile strength was expressed in centinewtons (cN), and elongation at break was expressed as a percentage (%).

5. Result & Discussion

This chapter presents & analyze the properties of fabric produced using air-covered yarns, tested according to different standards. The aim was to evaluate how the unique yarn structure influences key fabric performance characteristics.

5.1 GSM Analysis

Table 15. GSM values of different samples

5.2 Bursting Strength Test (ISO13938-2)

Table 16.Bursting Strength Analysis

5.3 Air Permeability Test (ASTM D 737)

Table 17. Air Permeability Analysis

5.4 Microscopic Analysis of Yarn

5.5 Single Yarn Strength Test

Table 18. Black Polyester +Viscose

Table 19. White Polyester + Viscose

5.6 Microscopic Analysis of Fabric

Table 20.Microscopic View of Fabric Samples

Sample	Sample Catalogue	Microscopic view of fabric
74 S/2(75D Recycle White Polyester (36 F) +70D Lycra
92 S/2 (75D Black Polyester (36F) +40D Lycra
49 S/3 [42 S EVS+42 EVS+ 75D White Polyester]
57 S/3(40S Cotton+ Lyocell (60+40) Melange Rose Color + 75D Recycle Poly (36 F) + 70D Lycra)
46 S/3 [40S EVS+40EVS+75D (36F) Black polyester

5.7 Fabric Construction Analysis

Table 21. Fabric Construction

5.8 GSM Analysis

The properties of the knitted fabrics produced using air-covered yarns were found to be strongly influenced by fiber composition, yarn structure, and the presence of elastane. Variations observed in GSM, bursting strength, and air permeability highlight the significant role of yarn fineness and fabric compactness in determining overallfabric performance.

The variation in GSM among the samples can be attributed mainly to differences in yarn count, fiber blend, and elastane content. Fabrics containing Lycra exhibited higher GSM values due to elastane-induced loop contraction, which increased fabric density and mass per unit area. Samples incorporating cotton and lyocell staple fibers showed comparatively higher GSM than polyester-only samples, as staple fibers contribute greater bulk and mass. Conversely, fabrics produced without elastane and using finer yarns demonstrated lower GSM, indicating that yarn fineness and elastane absence reduce fabric weight.

5.9 Bursting Strength

Bursting strength in textiles is the maximum perpendicular pressure a fabric can withstand before rupturing, typically measured in kilopascals (kPa) or psi using diaphragm or ball methods. Here, both sample shows Bursting Strength of 188 & 213.7 Kpa.

Bursting strength results revealed that fabric strength is influenced by yarn linear density and fabric compactness. The sample containing comparatively coarser EVS yarns demonstrated higher resistance to multidirectional stress than the finer-yarn sample.

The presence of elastane yarn in knitted fabrics improves bursting strength by enhancing elastic recovery and enabling better stress distribution within the knitted loop structure. [1]

The knitted structure, combined with air-covered yarn construction, allowed the fabric to withstand applied pressure by distributing stress evenly across the loops.

Due to limitations in sample width, bursting strength testing could not be performed on all samples; therefore, the observed results represent indicative trends rather than a comprehensive comparison. Nevertheless, the available data suggest that air-covered yarn fabrics possess adequate strength for stretch and comfort-oriented applications.

5.10 Air Permeability

Air permeability results indicated that the tested air-covered yarn fabrics are highly breathable. The open loop structure of the knitted fabric, together with the micro-spaces created by the air-covered yarn construction, facilitated efficient airflow through the fabric. Both tested samples exceeded the threshold for high air permeability as defined by ASTM standards, confirming that air-covered yarn fabrics are suitable for applications requiring enhanced comfort and ventilation.

Air permeability of elastic knitted fabrics is strongly affected by loop geometry, yarn linear density, and elastane content, where increased fabric compactness generally leads to reduced airflow through the fabric structure. [2]

Although air permeability testing was limited to selected samples due to sample size constraints, the consistently high values suggest that similar behavior may be expected across comparable fabric constructions.

5.11 Microscopic Analysis

Microscopicanalysis further supported the physical test results by revealing clear structural differences among the samples. Fabrics containing elastane yarn exhibited tighter and more compact loop formation, while samples without elastane showed a comparatively looser structure, indicating lower fabric compactness.

The yarn composition influenced surface characteristics: polyester filament-based yarns displayed smooth surfaces, whereas cotton–lyocell blends showed increased surface hairiness, contributing to fabric bulk. Micrographs also confirmed that the fabrics contained porous structures throughout the yarn and fabric cross-section, enhancing air permeability.

Air-covered and elastic yarn structures created micro-voids within the yarn and fabric, improving breathability without significantly compromising mechanical strength. These structural features correlated with variations in GSM, bursting strength, and overall fabric comfort, confirming that yarn composition, fiber blend, and air-covered yarn construction strongly influence fabric performance.

Overall, the analysis demonstrates that air-covered yarn structure, fiber blend, and elastane inclusion play a crucial role in determining the physical, mechanical, and comfort-related properties of knitted fabrics. Despite limitations in sample dimensions for certain tests, the findings provide meaningful insight into the performance characteristics of air-covered yarn knitted fabrics.

5.12 Limitations of the Study

The present study encountered certain limitations related to fabric production and sample preparation. The fabrics were produced using a small-diameter circular knitting machine, which inherently restricts the achievable fabric width. As a result, large-width fabric samples required by several standardized testing methods could not be produced.

Due to this limitation, insufficient fabric width and limited sample dimensions prevented the execution of certain physical and mechanical tests on all fabric samples. In particular, bursting strength and air permeability tests were conducted only on selected representative samples, while abrasion resistance and pilling tests could not be performed, as the available fabric sizes did not meet the minimum requirements specified in the respective testing standards.

Despite these constraints, the tests that were successfully carried out provide valuable insights into the effect of air-covered yarn structure, fiber composition, and elastane content on fabric properties. The results obtained should therefore be interpreted as indicative performance trends rather than exhaustive comparative evaluations.

Future studies may employ larger circular or flat knitting machines to produce wider fabric samples, enabling comprehensive testing across all performance parameters.

5.13 Application

Air-covered yarn combines an elastic core (usually spandex/LYCRA) with other fibers (polyester, cotton) using compressed air. This gives stretch, comfort, durability, and shape retention .in fabrics. 6

5.13.1 Apparel & Fashion

• Sportswear & Activewear – leggings, compression shirts, performance pieces that require stretch + recovery.
• Denim & Casual Wear – stretch jeans, fitted trousers.
• Seamless Knit Garments – seamless tops, bottoms due to smooth covered yarn construction.
• Tights & Hosiery – elastic socks, stockings with good recovery & fit.

5.13.2 Technical & Specialty Textiles

• Sportswear & Activewear – leggings, compression shirts, performance pieces that require stretch + recovery.
• Medical Textiles – compression bandages, support garments.
• Upholstery & Home Textiles – stretch seating, decorative fabrics, bedding.

5.13.3 Woven & Knitted Fabric Industries

Used broadly in both circular and flat knitting, seamless knitting, and woven fabric manufacturing to add elasticity to the final fabric.

6. Conclusion

The present research investigated the influence of yarn composition on the performance of knitted fabrics, focusing on five air-covered yarn samples with varying fiber combinations. The study demonstrates that yarn composition plays a fundamental role in determining fabric properties, including mechanical strength, extensibility, dimensional stability, surface appearance, and comfort. Variations in fiber type—natural, regenerated, synthetic, and elastomeric—affect the yarn’s behavior during spinning and knitting, which in turn influences the final fabric performance. For example, fibers with higher tensile strength and elasticity contributed to improved stretch and recovery in the knitted fabrics, while regenerated and natural fibers enhanced handle, softness, and moisture absorption.

The use of air-covered yarn technology allowed the production of uniform, high-quality yarns while minimizing processing variability. This method facilitated a systematic evaluation of how different fiber blends and yarn structures affect knitted fabric properties. The findings reveal clear trends in how specific combinations of fibers can optimize performance characteristics. Fabrics produced from yarns containing elastomeric cores exhibited superior stretch and recovery, whereas blends with regenerated or natural fibers improved comfort and hand feel without compromising dimensional stability.

Overall, this research underscores the importance of understanding the interrelationship between fiber properties, yarn structure, and fabric performance. By carefully selecting and combining fibers in yarn production, textile manufacturers can develop fabrics tailored for specific applications, ranging from everyday apparel to high-performance and functional textiles. The insights from this study provide a foundation for future work in optimizing composite yarn design, exploring novel fiber blends, and advancing knitted fabric technology to meet evolving industry demands.

6.1 Key Findings

The knitted fabrics produced from air-covered yarns demonstrated high air permeability, which can be attributed to the loop formation and the structural arrangement of the yarns. Fabric weight measurements indicated low GSM values, confirming that the fabrics were lightweight and capable of maintaining good airflow. Bursting strength tests revealed that the fabrics were strong, elastic, and suitable for various knitting applications. Microscopic analysis showed that the covering yarns were loosely packed, creating small gaps that further contributed to fabric breathability. Overall, the results highlight a clear relationship between yarn structure and fabric performance, indicating that knitted fabrics made from air-covered yarns are well-suited for a wide range of textile applications.

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Mazharul Islam Kiron

Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. Mr. Kiron is working as a textile consultant in several local and international companies. He is also a contributor to Wikipedia.

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