Introduction
Stretch fabrics have become common in foundation garments, sports apparel, denim, swimwear, and fitted fashion pieces. Much of that performance comes from spandex, the elastic fiber that allows textiles to stretch and recover quickly. It was first introduced in the United States in the late 1950s and drew attention because it was stronger and more durable than rubber. Today, it is still the most widely used synthetic elastomeric fiber and is usually blended with other fibers to improve comfort, fit, and shape retention.
What Is Spandex Fiber?
Spandex is a manufactured fiber in which the fiber-forming substance is a long-chain synthetic polymer made of at least 85 percent segmented polyurethane. The generic name elastane is used globally for these fibers, and elastane is also acceptable in the United States. The name spandex was coined by rearranging the syllables of the word expand.
Spandex is a block copolymer with rigid aromatic segments linked by urethane bonds to polyether or polyester segments. It is sometimes described as polyether spandex or polyester spandex, although the latter should not be confused with polyester/spandex blended fabric. At room temperature, the fiber can be stretched repeatedly to at least twice its original length and then return quickly to nearly its original length when the load is removed.
In the polyurethane structure, the polyether or polyester segments are amorphous and assume a randomly coiled position when the fiber is relaxed. When the fiber is stretched, those coils straighten and create the high elongation that spandex is known for. After the tension is released, the soft segments coil again and return the fiber to its prestretched length. The rigid urethane segments form hydrogen-bonded crystalline areas that prevent the polymer chains from sliding past one another and deforming permanently. The chains can also be crosslinked to add further integrity.
Manufacture and Physical Structure of Spandex Fiber
Spandex is manufactured in a process similar to that of aramid fibers. In one method, the constituents for the block copolymer of polyether and urethane are reacted in solution at a fairly low temperature, and the fibers are then dry spun from a dimethyl formamide solution. As the fibers come into contact while they are still soft and tacky, they fuse randomly into bundles that strengthen them for later processing. Another production method, called reaction spinning, begins with a shorter prepolymer that is extruded into a wet spinning bath. A compound then completes the polymerization of the long-chain molecules and partially coagulates them into fibers, and a later heating step completes the fiber formation. Because the fibers are still somewhat soft when they touch, they also form fused bundles.
Spinning solution additives can include delustering agents, dye receptors, whiteners, and lubricants. Spandex is produced as monofilament or fused multifilament yarns in several deniers. Monofilaments are usually round in cross section, while fused multifilaments are coalesced or partly fused together at intervals. Lycra® spandex fibers are round in cross section and smooth in the longitudinal view, while other spandex fibers may have peanut or dog-bone shapes. Rubber monofilaments have a rectangular cross section. Spandex can be made in much finer deniers than rubber, which gives it a clear advantage in many end uses.
Deniers range from 20 to 4300. Twenty-denier spandex is used in lightweight support hosiery that requires a large amount of stretch, while much coarser yarns of 1500 to 2240 denier stretch less and are used for support in hosiery tops, swimwear, and foundation garments. Spandex has a moderate density, and its specific gravity varies with pigmentation. It is usually white or gray and is often delustered.
Properties of Spandex Fiber
Mechanical Properties
Spandex is quite weak compared with nonelastomeric fibers, but it is much stronger than rubber. Its breaking strength is around 0.7 g/d. The modulus of spandex is extremely low, so it can be stretched easily. The most important property of spandex is its high elongation and excellent recovery. It can stretch 500 to 600 percent without breaking, and its recovery is comparable to that of rubber.
Chemical and Heat Properties
The moisture regain of spandex is low, about 0.75 to 1.3 percent, although water will still penetrate the fiber. Spandex will burn, and it melts at about 450°F. It becomes sticky at around 340°F, but it can be heat-set and dried safely in an automatic dryer. It is thermoplastic, with a melting point of about 446°F to 518°F.
Its resistance to chemicals is generally good and is one of the advantages it has over rubber. Strong concentrations of chlorine compounds can degrade the fiber and yellow it, although polyether-based fibers can better withstand chlorine levels used in swimming pools. Chlorine bleaches should be avoided. Seawater has no deleterious effect on spandex fibers. Perspiration and oil-based sunscreens do not seriously affect it, although some may yellow white fibers.
Spandex is dyeable with the same dyes used for nylon. That is an important contrast with rubber fibers, which are not dyeable and may grin through in a stretch fabric. Spandex is also resistant to dilute acids, alkalis, and dry-cleaning solvents.
Appearance, Comfort, Durability, and Environment
Spandex is seldom used alone in fabrics because other fibers usually provide the desired hand and appearance. Even in power-stretch fabrics for foundation garments and surgical hose, where beauty is not the main concern, nylon, cotton, or other fibers are often used. Because spandex is dyeable and has good strength, it can produce sheer garments in fashionable colors and prints without needing cover yarns. Eliminating the cover yarn reduces cost and fabric weight and gives a lighter, more comfortable fabric. In uses where spandex will touch the skin, however, it is normally covered.
Spandex has moderate comfort properties. Its moisture regain is low, so it is not especially comfortable in direct skin contact by itself. Even so, lighter-weight foundation garments made with spandex can give the same holding power as heavier rubber garments. It also has good appearance retention, resists soiling, and has excellent elasticity and elongation properties. Spandex has good resiliency and dimensional stability, so items retain an attractive appearance. Over time, however, coarser spandex fibers may rupture and work through the fabric. When the ends of those thick fibers appear at the surface, the fabric has lost some of its elasticity and elongation. This problem, known as grin-through, cannot be remedied and occurs most often in products that have aged or been stressed to extremes.
Spandex has moderate durability, but it is more resistant to degradation than rubber. It resists body oils, perspiration, lotions, and cosmetics that often damage rubber. It also has a good shelf life and does not deteriorate as quickly with age. Its flex life is much greater than that of rubber, which is one reason it became so widely adopted.
Spandex has satisfactory resistance to microorganisms. Extended exposure to light may discolor some white spandex, but it does not seriously deteriorate the fiber.
Uses of Spandex in Apparel and Textiles
Spandex is always used in conjunction with other fibers. The combination may appear as bare yarn, single-covered wrapped yarn, double-covered yarn, or core-spun yarn. Fine-denier spandex is especially useful for giving stretch with sheerness in products such as ladies’ hosiery.
Bare-core spandex yarns are uncovered filaments. They may be woven or knitted into fabrics in combination with other yarns. This adds strength to the spandex and gives stretch to the fabric. To make the monofilament more comfortable and more comparable to other yarns, a spandex filament core is often covered with another fiber. Single-covered yarns have one layer of another filament fiber wrapped around the spandex core. In double-covered yarns, one layer is twisted around the core in one direction and a second layer is twisted in the opposite direction. These yarns can be very sheer and are often used for support hose. Where it is useful, two different fibers can be used, one in each layer. The wrapped yarns stretch and recover with the spandex core. Core-spun yarns are made by holding spandex filaments under tension while a staple fiber is spun around the core.
Spandex supports, shapes, or molds the body, or keeps textiles from stretching out of shape during use. It is used primarily in knit foundation garments, actionwear, compression sportswear to reduce chafing and friction, intimate apparel, shapewear, hosiery, interiors, and narrow fabrics. It is also used in chlorine-resistant and competitive swimwear, skiwear, leotards, dancewear, leggings, biking shorts, and other body-fitting apparel. Spandex yarns are woven or knitted into a wide range of garments where stretch is desirable. These have included power nets for foundation garments, woven or crocheted fabrics for underwear waistbands, tricot or circular knits for lingerie, and activewear for swimming, skiing, golf, and tennis.
Spandex is increasingly seen in denim jeans, casual and dress pants, knitted and woven shirts, and tops, where a small amount gives extra comfort and fit. Formerly, stretch-textured yarns of nylon or polyester were adequate, but the current preference for the look and feel of natural fiber fabrics has made this alternative more appealing. In practice, that balance of stretch and comfort is hard to match.
Spandex is an expensive fiber, so its cost must be considered when developing apparel products. The amount used in blends reflects that cost. Jeans or a sport coat may contain only 2 to 5 percent spandex, where the effect is a slightly better fit. Activewear and swimwear often contain 10 to 15 percent spandex, while support garments use greater amounts. Blends of 2 percent to 40 percent spandex with other fibers are common. If a synthetic fiber blend is needed, cheaper polyester/spandex blends are less widely used than nylon because spandex is damaged in water at temperatures higher than 220°F. Spandex/nylon blends can be dyed with the same dye at a lower temperature and also provide better stretch and recovery properties.
Spandex Trademarks and Market Names
Lycra® fibers have dominated the spandex market. Other brand names include Roica®, developed by Bayer and now produced in Germany by the Asahi Kasei Group, and Glospan®, manufactured by RadiciSpandex. The number of spandex producers has increased greatly as spandex has become more of a commodity product. Better-known manufacturers have responded by marketing the quality of their products, as seen in Lycra® hang-tags on many garments.
Care Guide
Because spandex is usually used with other fibers, care must consider both the spandex and the companion fiber. Spandex should not be exposed to very hot water or to excessive heat during ironing. Ironing temperatures should not exceed 300°F, or the synthetic setting on a hand iron. Dryer temperatures should be moderate. Chlorine bleaches should not be used in laundering spandex because they can degrade the fiber.
Spandex can be machine-washed or dry-cleaned, depending on the other fibers in the fabric. It is resistant to dilute acids, alkalis, and dry-cleaning solvents, but harsh laundering conditions can still shorten its life.
Conclusion
Spandex remains the key elastic fiber because it combines high elongation, excellent recovery, and better durability than rubber. Its segmented polymer structure gives the fiber the stretch it needs, while the rigid segments help it return to shape. It performs best in blends, where it can improve fit, comfort, and appearance without overwhelming the fabric. As demand for stretch garments continues to grow, spandex will keep playing a central role in textile performance.
