Ping pong balls are made from a celluloid material and filled with a gas to improve the degree of bounce. They are generally finished in a matte white or orange color and tested in accordance with an overall quality rating.
Ping pong balls are given a star rating between one and three, depending on consistency, bounce and roundness. The star rating is marked on the ball, with a three-star rating implying the highest quality. Ping pong ball sizes can vary, but the International Table Tennis Federation standardized the size in 2000, declaring that only balls with 40 millimeter diameters should be used.