Superior Threads - Prolock #303 Natural White. Textured Polyester Textured Polyester 8,500 yd Cone ProLock is colorfast and can be laundered commercially without fading. ProLock is resistant to chlorine which makes it the best choice for childrens clothing as well as swimming and active wear. (ProLock is Oeko Tex 100 certified) The concern of yellowing associated with weathering and aging of "woolie-type" nylon products is avoided with ProLock.