The special properties of the rubber are seen by the external material surface weaving and to a lesser degree from the kind of sponge used (for rubbers with sponge). The rubber surface plays an important role in its special properties. In this category we have pimples-out rubbers and inverted rubbers.
The pimples-out rubbers differ in the shape and size of the pimples. There are rubbers with conical or cylindrical pimples and large or small pimples. Each one of these has different characteristics. For example, the big, short pimples give greater speed and spin to the ball whereas small, long pimples have the opposite effect on the ball.
The inverted rubbers differ in terms of degree of friction. Generally speaking, this type of rubber gives a greater spin to the ball compared to pimples-out rubbers. This is because inverted rubbers have no gaps on the surface and so there is more rubber contacting the ball. These rubbers, however, come second in speed compared to short pimples-out rubbers. This is because with inverted rubbers, the ball gains speed that comes only from the sponge pressure, while with pimples-out rubbers the final speed of the ball is not only given by the sponge but from the pimples as well.
The rubbers that do not spin the ball are of a special category. These and some types of pimples-out rubbers are used by defensive players and offer good control against offensive strokes. Before the implementation of the bicolor regulation (one side of the racket has to be red, the other black), using different rubbers on the same racket was a great weapon of the defensive player who could easily trick his opponent by altering the side of the racket he used. These players would spin the racket by the handle so their opponents could not keep track of which side they were using for the forehand or the backhand stroke.
The sponge is a kind of porous pressured rubber with the addition of some chemical substances that form small gas vesicles, which give it certain specific characteristics. According to its density, weight and width, the sponge can give more or less speed to the ball. Generally the hard and thick sponges give greater speed to the ball and the soft and thin sponges have the opposite effect. The major factor affecting ball speed, however, is the weight of the sponge, which is directly related to the sponge thickness. That is why the offensive rubbers are harder and heavier than the defensive ones. The thickness of the sponge varies from 1-2.5mm (0.04-0.1in) while the total “sandwich” rubber thickness must be no more than 4mm (0.16in).
It is necessary for a table tennis player to know the characteristics of rubbers. Firstly, because he should be able to choose the appropriate one for his own playing style and secondly because he must know how to counter opponents using different rubbers.
The coach knows more on this subject because he must guide the player in choosing a rubber with attributes suited to his playing style and he must instruct the player in how to counter opponents who use rubbers with different attributes. The coach must follow some rules to vouchsafe the proper instruction of the basic techniques for the beginner. On the other hand, the seasoned player has adopted his own specific playing style, and only he can choose the blade and rubbers that suit him.
Rubber care
The specific qualities of a rubber are lost over time. With proper use, the rubbers retain their qualities for a longer period. Exposing the rubbers to the sun and to high temperatures should be avoided and after each match the rubbers should be cleaned with cotton and water. There are special cleaning fluids available but using them frequently can destroy the surface of the rubber. For this reason these fluids must be used before a match only.
Info From : http://www.tabletennis.gr/articles/details.asp?id=8
