 Wartime production during World War II required vast amounts of cotton , silk , nylon , wool , leather , and rubber . In 1942 , the United States War Production Board issued Regulation L @-@ 85 , cutting the use of natural fibers in clothing and mandating a 10 % reduction in the amount of fabric in women 's beachwear . To comply with the regulations , swimsuit manufacturers removed skirt panels and other attachments , while increasing production of the two @-@ piece swimsuit with bare midriffs . At the same time , demand for all swimwear declined as there was not much interest in going to the beach , especially in Europe . 
