●Americas #1 selling ball: 100 years of testing and completed product. Penn Championship is Americas best selling tennis ball ●Pen Performance: Controlled fiber release ensures perfect nap and natural rubber reduces consistent feel and impact. Championship lines deliver unrivaled consistency every time you hit the court ●ALL COATS: The extra duty tennis ball is great for hard court games, but can be played indoors or outdoors on soft clay courts ●OFFICIAL BALL: Penn Championship is the Official Ball of the USTA League You will know you are playing with a high quality and stable ball. Available in Extra Duty Felt, Regular Duty Felt, or Extra Duty Altitude Felt. USTA and ITF approved ●LONG LASTING DURABILITY: The interlocking wool fibers allow any court tennis ball to look as good as new