The international rules specify that the game is played with a light 2.7 gram, 40 mm (formerly 38 mm) diameter ball. The ball is required to have a coefficient of restitution of 0.4. The 40 mm ball was introduced at the 2003 World Table Tennis Championship. However, this created some controversy as the Chinese National Team complained that this was merely to give non-Chinese players a better chance of winning. A 40 mm table tennis ball is slower and less "spinny" than a 38 mm one. The ball is made of a high-bouncing gas-filled celluloid ball, colored white or orange, with a matte finish. The choice of ball colour is made according to the table colour and its surroundings. For example, a white ball is easier to see on a green or blue table than it is on a gray table.