 Bikinis can and have been made out of almost every possible clothing material , and the fabrics and other materials used to make bikinis are an essential element of their design . Modern bikinis were first made of cotton and jersey . DuPont 's introduction of Lycra ( spandex ) in the 1960s completely changed how bikinis were designed and worn , as according to Kelly Killoren Bensimon , a former model and author of The Bikini Book , " the advent of Lycra allowed more women to wear a bikini ... it didn 't sag , it didn 't bag , and it concealed and revealed . It wasn 't so much like lingerie anymore . " Alternative swimwear fabrics such as velvet , leather , and crocheted squares surfaced in the early 1970s . 
