What are the characteristics of the two sides of the table tennis bat in use?

One side is smooth and the other side is granular rubber, which will make the return ball rotate and have different strength when using each side, thus causing great discomfort to the opponent.

However, according to ITTF rules, both sides of the racket must be black and red. This is because there are too many kinds of rubber, including positive rubber, long rubber, raw rubber, reverse rubber and so on. If they are all black, you can't tell what kind of rubber your opponent uses in the game, and you can't tell the opponent's ball path and rotation. In this way, the opposing sides can know what kind of rubber they use when hitting the ball through color discrimination, so as to achieve the purpose of fair play.