Introduction
Yarn structure is one of the most important factors influencing the performance of textile fabric. Performance of textile products is affected by interactions among the fibers used, the yarn structure, the fabric construction, and any finishes applied. In practice, the same yarn can behave differently in a woven fabric than in a knit, so yarn structure should always be matched to the final end use. Key properties of yarns and their effects on the durability, appearance, and comfort of textile fabrics are presented below.
Fabric Durability
Yarn Strength
Yarn strength is of primary importance in determining ultimate fabric strength. Yarn strength is due not only to the inherent strength of the fibers in the yarn, but also to the yarn structure.
Filament Yarns vs. Spun Yarns
Filament yarns are stronger than spun yarns because all of these continuous fibers are contributing to yarn strength. The yarn breaks when the fibers are ruptured.
Spun yarns, which are held together by their twist, are broken by breaking some fibers and by overcoming the twist frictional force holding the fibers together. This takes less force than breaking all the fibers in a comparable filament yarn. For this reason, filament yarns are often selected where smoothness and strength are both important, while spun yarns are preferred when bulk or a softer surface is needed.
Twist and Yarn Strength
As twist is increased in spun yarns, the strength increases (up to a point) because the increased frictional force between fibers prevents slipping. Overtwisting, however, will decrease strength due to increased strain on the yarn.
The best twist level is usually confirmed by testing the specific fiber blend, because the optimum point changes with yarn size, fiber length, and fabric construction.
Yarn Size
Coarser yarns can withstand tensile forces better than finer yarns and normally contribute more to fabric strength.
Stretch and Recovery
The elongation and recovery of fabrics are important in determining their end use and performance. Fabrics that stretch and recover are comfortable and are especially appropriate in products such as hosiery or swimwear.
In order to produce yarns with maximum elongation, elastomeric fibers such as spandex or rubber that stretch up to five times their length (500 percent) and recover can be used, according to the LYCRA Company technical data. Filament yarns can be textured to provide stretch.
Abrasion Resistance
Resistance to abrasion is determined by the ability of a material to absorb the energy applied during abrasion. A number of textile properties affect the resistance of a fabric to abrasion, yarn construction being one.
Loosely twisted yarns abrade more easily than do tightly twisted yarns. In the loosely twisted yarns, individual fibers are more likely to be plucked out of the fabric surface. Loose, hairy yarns also tend to pill more readily, so abrasion resistance and appearance are closely linked in everyday wear.
Fabric Appearance
Drape
Drape refers to the ability of fabric to form pleasing folds when bent under its own weight. Drape is improved by yarn structures that allow movement or bending within the fabric.
Twist also affects the bending of yarns. Highly twisted yarns bend more easily because the fibers are oriented at a sharper angle to the yarn length. This behavior is especially apparent in crepe yarns, which are highly twisted. True crepe fabrics, those made from crepe yarns, have high drapability. Designers use this effect in garments such as scarves, dresses, and skirts where a fluid fall is desired.
Fabric Hand
Fabric hand refers to the “tactile sensations or impressions that arise when fabrics are touched, squeezed, rubbed, or otherwise handled”. Hand is an important consideration in consumer selection and acceptance of apparel fabrics. Like drape and other properties, it is a complex phenomenon involving a number of different fabric characteristics.
One important factor in the assessment of hand is the smoothness of the material. Filament yarns and combed spun yarns feel smoother than textured or crepe yarns. In addition, a fabric that compresses easily and recovers from compression or squeezing will feel soft. This feeling is enhanced by resilient fibers and high-bulk yarns that are not compact.
A fabric’s hand can also change after finishing, scouring, brushing, or heat setting, so the yarn is only part of the final tactile result.
Wrinkle Resistance
Yarn properties must be considered in relation to wrinkle recovery. When a crease forms in woven or knitted fabric, the yarns bend. Yarn stiffness, or resistance to bending, is related to twist and size.
In looser yarn structures, with lower twist, fibers are freer to move to relieve the stresses of bending. They will, therefore, bend relatively easily. In more tightly twisted yarns, the frictional forces within the yarn tend to keep fibers from shifting position, and they tend to return to their original configuration and resist wrinkling. As described earlier, however, overtwisted yarns bend more easily.
The most flexible yarn of all should be one in which filaments are combined with little or no twist. The least flexible yarns should be those in which the fibers are bonded together by an adhesive or fused by heat or chemical means.
Yarn size affects stiffness as well. Heavier yarns resist wrinkling more than finer yarns. In practice, wrinkle resistance is usually best when yarn size, twist, and fabric density are balanced rather than maximized in one direction. Yarn size can be increased by putting a larger number of fibers into a yarn, by using fibers of larger diameter, or by plying several yarns. Utrafine fibers, even in coarse yarns, however, reduce resistance to bending.
Covering Power
The terms covering power and cover factor refer to both the optical and geometric properties of fabrics. Optical covering power is the ability of the fabric to hide what is placed under it. Fiber characteristics affect the optical covering power. So, too, does yarn structure.
Smaller-diameter yarns or smoother yarns cover less well, depending on how tightly packed the yarns are in the fabric structure. If opacity is a priority, a tighter fabric construction and a larger yarn diameter usually improve cover more reliably than yarn smoothness alone.
Fabric Comfort
Thermal Comfort
Heat transfer is the transfer of heat energy from a generating body to the surrounding atmosphere. Textile fabrics can provide resistance to heat transfer from a body, or in the case of some interior furnishings, from buildings. As noted earlier, trapped air keeps heat near the body.
Yarn structure and its related property of fabric thickness are extremely important in determining the thermal comfort of fabrics. A spun yarn or textured filament yarn entraps more air than a flat filament yarn and, therefore, offers more resistance to heat transfer. The degree of twist also affects thermal comfort as the higher-twist yarns hold less air volume.
This is why bulky spun yarns and textured filament yarns are common in cooler-weather fabrics, while flatter yarns are often used when heat buildup must be reduced.
Air Permeability
Air permeability is the ability of air to pass through a fabric. Where openings between yarns or between fibers within yarns are large, a good deal of air will pass through the fabric. Conversely, when compact yarns are packed tightly into fabrics, with little air space between them, the flow of air through the fabric is diminished.
It follows, then, that closely woven fabrics with compact, tightly twisted yarns have lower permeability. Open knits and looser weaves usually feel cooler because they allow more air exchange than tightly packed constructions, even when the same fiber is used.
Fabric Softness
Yarns contribute to fabric softness. Loosely twisted yarns and many novelty yarns have rougher surfaces that decrease the smoothness of fabrics. Filament yarns are generally smoother than spun yarns.
A yarn can still feel soft even when it is not the smoothest, because low twist and lofty structure often matter as much as surface finish. Sheets made of filament silk yarns are softer and more luxurious than those of staple linen or cotton fibers.
Key Takeaway
Yarn structure is a major driver of fabric strength, appearance, and comfort, so selecting the right twist, size, and yarn type is one of the most practical ways to control fabric performance.
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.
