Check the listing for details. Penn Championship Regular Duty Felt Tennis Balls Brand NEW Lot. Condition: New. Listed at 13.95 USD. The Penn Championship Regular Duty tennis ball is the No. 1 selling tennis ball in North America. These balls are manufactured under strict quality control standard and using only high quality materials. Approved by the International Tennis Federation, the Penn Championship ball is designed for use on hard court surfaces.Features:Natural rubber for consistent feel and reduced shockInterlocked wool fiber for longer wear and increase durabilityDeep elastic seams for reduced cracking and longer wearControl fiber release for consistencyApproved by the International Tennis Federation (ITF) and United States Tennis Association (USTA)Recommended for hard court surfacesAll balls are factory sealed and pressurized. Guaranteed authentic, and brand new.