) The Penn Championship Extra Duty Felt pressurized tennis balls come in a pack of 2 cans, containing a total of 6 balls. These balls are made of extra-duty felt, which makes them ideal for hard court play. The natural rubber offers a consistent feel and reduced shock, while the interlocked wool fiber provides longer wear. The deep elastic seams prevent cracking, and the USTA/ITF has approved these balls for competitive play.