Penn Championship is America?s #1 Selling Tennis Ball and represents the standard by which all other tennis balls are measured. It features a controlled fiber release for consistent nap, natural rubber for consistent feel and reduced shock, and interlocked wool fiber for longer wear. Penn Championship is the Official Ball of USTA Leagues. It is USTA and ITF approved and is available in extra-duty felt, regular duty felt, or extra-duty high altitude felt. The Championship Line provides quality play every time you hit the court.