Book 28, Question 44
Why do table tennis paddles have rubber with pimples?
Table tennis paddles are covered in thin rubber over sponge.
Some have tiny bumps called pimples that face out or in. Smooth rubber grips the ball and makes lots of spin, while pimples change the spin and make shots unpredictable. Players choose rubbers that suit their style. The sponge underneath gives spring, and rules control the thickness.