The best platter pad I have ever seen was made by Warren Gehl, who is currently working at Audio Research. His platter pads are now pushing 20 years old but are still getting good resale prices when they show up.
The issue here is the durameter (hardness) of the LP vs that of the platter pad. Too hard = bright, too soft = no bass in a nutshell. When the two are the same hardness, the pad is able to absorb vibration from the LP. Now this is important- put an LP on and turn down the volume. The better the pad, the less you will hear coming off of the surface of the LP itself. If you think that is not talking back to the stylus you would be quite mistaken!
Once the pad has absorbed this vibration, it cannot reflect it back to the LP. On top of that, the stylus exerts considerable pressure on the LP surface! 1.5 grams may not seem like much, but given the size of the needle its like several hundred pounds per square inch! The result is that the LP depresses slightly within the immediate vicinity of the stylus. The platter pad must support this and not also depress.
Finally, its good if the pad also provides some damping to the platter, without that function interfering with its ability to damp the LP.
Most pads are too hard- any metal, acrylic, glass and the like. Of the list above, delrin is the closest. IMO its unfortunate that Warren no longer makes his pad. When he did, what we found was that as long as the 'table could manage the weight, that table would sound instantly better (better bass, smoother more detailed highs) than any table without it.
I've been thinking that the thing to do is to build a pad out of a blank LP, bonded to a damping product that has a metal substrate, perhaps stainless or aluminum. This would have the correct hardness, being the same material, and the damping control at the same time...
