I recently saw an ad that offered glass fermentation weights for canning items. For some reason it set my mind to thinking about how I could use them as some sort of isolation pad for audio components such as my VPI HW-19 upgrade project. I then searched Amazon for sorbothane and found a set of pads of appropriate size for a good price. Here are the links to the items I purchased for a total of $27.
Sorbothane is great stuff. It is not very elastic and turns a great deal of energy it receives into heat. You can get it in other shapes and durometers as well including sheets that I have used. To isolate it from wooden surfaces I have used aluminum foil at the interface which very effectively eliminates any bleed through. For isolation of my turntable I made a box for under the turntable out of MDF that is filled with sand and veneered with American walnut. That rests on sorbothane feet. The resulting high mass and high compliance yields a very low resonant frequency isolating all but the most subsonic vibrations. The sorbothane also greatly attenuates the energy.