Penn Championship Tennis Balls - Extra Duty Felt Pressurized Tennis Balls100% Wool Imported AMERICA'S #1 SELLING BALL: The product of 100 years worth of testing and perfecting; Penn Championship is the best selling tennis ball in America. PENN PERFORMANCE: Controlled fiber release provides perfectly even nap, while natural rubber offers consistent feel and reduced shock. The Championship line provides unparalleled consistency every time you hit the court. ALL COURTS: While extra duty tennis balls are best suited for hard