Dear Wiggo said:
When I played, it was pips in for spin, and 7mm of rubber backing between the blade and the outer layer for speed ;-)
If my memory is correct (1980-1990 era, regulation probably changed a bit):
Black and red side, even if the rubber is identical on both sides.
1. Pips in with thick layer (For example Shriver) for effect and speed (offensive)
2. Pips in with thin layer (for example Flextra) for effect and control (defensive)
3. Pips in, extra smooth with thin layer. Better known as Anti spin. (defensive)
4. Pips out are generally low effect rubber combined with a thick sandwich! The result was a very hardhitting ball with not much spin (offensive)
5.
Very long pips out! Very hard to control and very odd effect. If I remember correctly that was banned PRONTO. I think only one or two guys used it with devastating effect, but generally seen as gamebreaking (was near impossible to anticipate). It still exist in much less extreme forms, also known as funny rubber.
Of course there was also the issue of fresh versus dry glue, or even special "speed" glue, but the level I played we didn't have the money for that kind of sophisticate stuff, so I'm not very knowledgable there.
Also, some say red is faster but a bit less spinny as black rubber due to the color additives, but to discern those kinda differences is far, far beyond my skill
Back in the 80-90ies it was a bit of alchemy really, but the great stallwart rubbers survived most trends (for example Flextra and Shriver).