Description Set a standard on the court with Wilson US Open Extra Duty tennis balls! Enjoy unrivaled consistency and durability from these premium tennis balls. A high-quality woven felt supports extended play on hard or abrasive courts. It’s easy to see why the Wilson US Open Extra Duty is the trusted choice of the tournament for over 40 years. Ideal for longer play on hard court surfaces ITF and USTA approved Official Ball of the US Open Made with premium woven felt.