Expancel Inc. microspheres provide long-lasting bounce in Micro X series tennis balls from Tretorn Sweden AB of Helsingborg, Sweden.
Some 700 million microspheres take the place of compressed air in the balls approved by the U.S. Tennis Association. Conventional tennis balls lose a small amount of air each time the ball is hit by a racket, so over time the ball loses its buoyancy. By contrast, Expancel microspheres retain the ball's bounce, according to the Duluth, Ga., company.
Expancel microspheres comprise the Micro X ball's inner core. Surrounding the spheres is a core made of titanium and polybutadiene rubber, which gives a softer feel than in conventional balls and therefore enhances spin. A special felt surface covering the ball also helps aid playability and wear resistance.
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