Skinny jeans have been around since the 1950s, when the thigh-hugging style was donned by film stars like Roy Rogers and Marilyn Monroe. Spandex was not a staple of skinny jeans then, making them less comfortable than today's versions. Spandex, a stretchy synthetic fiber made from polyurethane, allows skinny jeans to cling to the body without restricting it. In 2010, jeggings hit catwalks, providing a jeans alternative with even more spandex -- and stretch -- than skinny jeans.

Spandex Equals Stretch

Today's skinny jeans usually include spandex in their mix of fabrics. Most skinny jeans contain between 1 and 10 percent spandex, with the remainder made from cotton and/or polyester. The composition of skinny jeans typically is either 79 percent cotton, 20 percent polyester and 1 percent spandex; 98 percent cotton and 2 percent spandex; or 90 percent cotton and 10 percent spandex. The higher the spandex ratio, the greater the stretch.