Speedo Launch Splice Cross Back Endurance+ Onepiece Swimsuit 50% Polyester/50% PBT Engineered from our exclusive, longest lasting and best-selling Endurance+ fabric: 100% chlorine resistant fabric designed to lasts 20 times longer than conventional swimwear fabrics. With open keyhole at the back and ultra-thin straps, our new Cross Back is comfortable yet provides support you need with the center back strap. Provides excellent support and freedom of motion.