I ordered Shore A durometer 90 polyurethane from McMaster - Carr. As a matter of fact, I made suppressor wipes from the same material, except I used 1/4" stock instead of 1/8" stock for that. I wouldn't go less than Shore A durometer 70. The buffers really take a beating, and anything softer simply won't last. As cheap as the material is, you could order a couple of different types and try them out. Neoprene also makes a good buffer (and a good suppressor wipe) You can even go with 3/16" or 1/4" for more buffer action.