Improve your game with these PENN Championship Extra-Duty High-Altitude Felt Tennis Balls. Approved by the USTA, they are designed to be easier to control in thin air and should only be used above 4000' elevation levels. These PENN Tennis Balls come in a set of 36 with 12 recyclable plastic cans. Each one features controlled fiber release for consistent nap and natural rubber for reduced shock. They are also made with interlocked wool fiber for longer wear.

• Used to play at high altitudes
• Only for play occasions above 4000' elevation levels
• Approved by the USTA
• Pack includes 36 high-altitude tennis balls in 12 recyclable plastic cans
• Do not store over 120 degrees Fahrenheit
• Controlled fiber release for consistent nap
• Made from natural rubber for reduced shock
• Interlocked wool fiber for longer wear
• Designed for easier control in thin air
• Penn Championship is America's number 1 selling tennis ball