These balls are officially used in some World Table Tennis (WTT) events, making them high-quality competition balls. Excellent Roundness and Hardness: They are known for very good consistency in roundness and wall thickness, producing true and predictable bounce. Durability: Better than average durability for a 3-star ball; holds up well in both training and match play. The 729 S40+ balls felt noticeably different from the three other WTT balls. The S40+ sounds significantly softer and feels lighter and faster and has the flattest and longest topspin trajectories.