a synthetic fiber formed from polyurethane solutions or melts or by chemical formation (polyurethane is prepared directly from a diisocyanate and diamine during fiber formation).
Spandex fibers sharply differ from natural fibers and other types of chemical fibers in physical properties. However, they are in many ways similar to rubber fibers. They are characterized by a great amount of stretch and a low modulus of elasticity. They are able to recover to original length over a very short period of time. Because spandex fibers, particularly in the stretch state, exhibit substantial strength losses at 120°C, fabrics made from them are cleaned and dyed at temperatures no higher than 90° C. The fibers turn yellow on exposure to light, whereas their other properties remain practically unchanged. Yellowing can be eliminated to a great extent with the aid of photostabilizers. Spandex fibers are resistant to hydrolytic agents during finishing, washing, and dyeing. They are also resistant to oils, acids, alkalies, and organic solvents containing chlorine.
Spandex fibers are processed in pure form or in a mixture with natural fibers or other types of chemical fibers. The added fibers are mainly used for wrapping the spandex fibers, thereby protecting the core fibers from the light. A yarn composed of 5–20 percent spandex fiber and 80–95 percent nonexpandable fiber is used to prepare fabrics for shirts, blouses, sportswear, coats, and corsets.
Spandex fibers are known by the trade names Lycra and Vy-rene (United States), SPA and Neoran (Japan), Spanzelle (Great Britain), and Vorin (Italy). In 1973, world production of spandex fibers amounted to tens of thousands of tons.