Spandex, Elastane or Lycra

From http://en.wikipedia.org/wiki/Lycra

Spandex or elastane is a synthetic fibre known for its exceptional elasticity. It is stronger and more durable than  rubber, its major non-synthetic competitor. It was invented in 1959 by DuPont chemist Joseph Shivers. When first introduced it revolutionized many areas of the clothing industry.

"Spandex" is a generic name and not derived from the chemical name of the fiber, which most manufactured fibers are, but derived by shifting around the syllables in the word expands. "Spandex" is the preferred name in North America; elsewhere it is referred to as "elastane" or by one of its most famous brand names - Lycra.

Lycra, a trademark of Invista (formerly part of DuPont). Such is the prominence of the Lycra brand that it has become a genericised trademark in many parts of the world, used to describe any kind of spandex. Invista discourages such use, protecting its trademark vigorously.