WILSON WRT101600 US Open Grass Court White Tennis Balls Case The Wilson US Open Grass Court tennis ball is the offical ball of the US Open since 1978. The US Open tennis ball is made with exclusive felt from Tex Tech Industries for superior playability, consistency, and durability. The white felt is made specifically for grass court surfaces. Also available are the Wilson US Open Extra Duty tennis ball for hard courts, Wilson US Open Regular Duty tennis ball for clay or indoor courts, or Wilson US Open High Altitude tennis ball for all court surfaces! Must ship to school address or country club. Tennis Balls | Wilson Tennis | Us Open Size - (See Description) | Color - (See Description) Authorized Wilson Dealer. All racquets are strung and ready for the courts! SEE SELLER DETAILS FOR RETURN POLICY.