The Penn Championship Tennis Balls are widely praised for their incredibly long lasting construction, which also helps preserve the freshness and playing characteristics throughout many tennis clashes. They feature an extra-duty, interlocked wool felt, which makes more visible and extremely durable, especially on the hard courts. This USTA (United States Tennis Association) approved tennis ball provides a controlled fibre release for a consistent nap, whereas the reduced impact shock comes from the natural rubber core. The balls are shipped as a large bundle of 6 dozen (72 tennis balls).