Celluloid is used to make ping pong balls. Celluloid is nitrated cellulose that has been mixed with camphor to give it the texture of plastic. They are generally finished in a matte white or orange color and tested in accordance with an overall quality rating.
Celluloid ping pong balls are filled with gas, which enhances their bounce rating and keeps them lightweight. Celluloid was previously used in making film and other plasticized items, but it is not used for those purposes as much today. Ping pong balls, some fountain pens and frames for some glasses are still made from traditional celluloid. Cellulose acetate is a common substitute for celluloid because the process of making celluloid can be dangerous due to the highly flammable nature of the components of celluloid.
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.