The Penn tennis ball is the #1 choice of Tennis players. Penn World Tour features tournament-grade felt and technical grade rubber core for precise bounces. The ball also features Smart Optic felt, which is 19% brighter than the regular felt. The brighter felt enhances accuracy due to increased visibility and lets your have additional time to prepare your shots. The Extra Duty felt is more durable in order to withstand the abrasive nature of hard courts.