The Penn ATP tennis ball is the #1 choice of ATP players and the offical ball of the ATP. Penn ATP features tournament-grade felt and technical grade rubber core for precise bounces. The ball also features Smart Optik 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. Also available is the Penn ATP Regular Duty tennis ball for clay or indoor courts. The Penn ATP Extra Duty tennis ball is USTA and ITF approved.