The sleek Nike Swim Color Block Power Back Tank cuts down on abrasion caused by repeated swimming movements, known as suit rubs. Nike NX is an incredibly durable, colorfast, chlorine-resistant nylon fabric that retains its shape and can withstand long seasons of training and competition. The smooth fit and minimal seam construction provides freedom of motion for all four strokes. Colors: Nike NX 81% nylon/19% spandex. White: 100% polyester. Imported.