The Nike Sport Band is made from a special high-performance fluoroelastomer with molded perforations for better ventilation. It is durable, robust, and surprisingly soft. The soft, dense material feels good on the skin and hugs the wrist. The innovative pin closure ensures a secure fit. You can mix and match most bands with any Apple Watch Series 3 case or newer cases of the same size. 41 mm bands fit 38 mm and 40 mm cases. 45 mm bands fit 42 mm, 44 mm, and 49 mm cases.