Pro Penn Marathon is Penn’s longest-lasting tennis ball featuring exclusive Encore™ Technology for a 22% longer-lasting core and high tenacity LongPlay® Felt for extended play. Pro Penn Marathon is the official ball of PTR because of its guaranteed longevity, durability, and visibility. Pro Penn Marathon is available in Extra-Duty Felt (for hard courts), Regular-Duty Felt (for soft courts), and Extra-Duty High Altitude (for higher altitudes). Penn’s Professional tennis balls are the most technologically advanced tennis ball providing players with top-of-the-line core and felt technologies that allow the ball to play at its best for longer periods of time.