Complex sentence: The principal occasion of use is the maritime holiday, where the most used material in the making of swimwear was the Lycra, born in 1958, and had the ability to stretch up to 7 times, and then returned to the original size.
Split into simpler sentences: The principal occasion of using beachwear was the maritime holiday, where the most used material in the making of swimwear was the Lycra that was created in 1958. It had the ability to stretch up to 7 times its original size, and then it could return to the original size.