The TYR Spectrum Thin-X Back Swimsuit is built with Durafast(TM) Stretch, which combines the durability and colorfastness of Polyester with excellent comfort and flexibility. This Poly-Spandex blend is ideal for training and able to sustain hours of abuse while maintaining a comfortable hold on your body. Durafast(TM) Stretch offers the same technical benefits of Durafast(TM) Polyester including unsurpassed sun and chlorine resistance, in addition to control and memory like you've never experienced before in a Polyester suit.