The Bi-Colour balls are designed in order to better judge the rotation trajectory of a ball, they are great for learning and understanding the spin on the ball, for use in coaching and training sessions. Two colours of hemisphere are combined into one. While the table tennis ball is under the high speed-movement, it will cause visual changing, which would increase the judgement on rotation. BI-colour ball was jointly developed by the Chinese Table Tennis Association (C.T.T.A.) and Double Happiness. They selected ABS as the material.