Medium Pimples Rubber
Medium pimples rubbers are a cross between long and short-pimpled rubbers. It is the pimple's length that makes it different from long pimples and short pimples. The medium pimples produce a more dead or knuckleball effect that causes opponents to place many returns into the net.
Thickness of Sponge
The thickness of the sponge will affect how fast the overall rubber will be, and also how much control it has. Thicker sponge is faster but has less control than thinner sponge. Most attackers use sponge of either 2.0mm or Max thickness (2.2mm), while many defenders use thinner sponge for the extra control. Most professionals use thicker sponge for increased speed.
It is possible to not use sponge at all with pimple out rubbers. This is classified as OX, using no sponge can be an effective tactic for those players who defend or twiddle their bats!