The Wilson US Open tennis ball is a gasfilled ball that is known for its superior qualities, consistency and durable design. The tennis ball can be used on all types of court and is ITF approved. The Wilson US Open tennis ball is the official ball of the fourth Grand Slam tournament of the season, the US Open in New York. For over 25 years this ball is used in this tournament which takes place at the end of August/ beginning of September. About 70.000 tennis balls are used during this event.