Spandex fibers are manufactured fibers formed from a long-chain synthetic polymer consisting of at least 85% segmented polyurethane. Spandex fibers are elastomeric fibers, which are stretchy and rubber-like substances. They have extremely high elongation, at least 200% and, in some cases, up to 800%. Rubber and spandex are the best-known elastomeric fibers.
Spandex is a segmented block polymer and has several cross-sectional shapes, of which the most common is a “dog bone” shape. The extrusion process results in some fusing of adjacent filaments to produce a coalesced filament yarn. Spandex fibers are very weak; however, the high degree of stretch allows for uses where the lack of strength is overcome. In apparel products, spandex is almost always used only in small amounts with other fibers to provide a desired degree of stretch.