Wilson US Open Ball x4 is the official ball of the US Open since 1978. The ball is made of high-grade extra duty felt that offers great performance on hard courts. The high-altitude core gives durability on clay, grass, or indoor courts. It has a weight, height, length, and width of 200gm, 8 cm, 21 cm, and 8 cm respectively. The ball is approved by USTA and ITF for competitive play.

- Suitable for grass, wet and hard ground
- Long-lasting and official ball
- High altitude core
- Approved by USTA and ITF