A sheet of carbon fiber material would probably be good as well. It's strong and non-resonant.
Arm board material?
I am thinking about making a new arm board for a TNT IV turntable. What material would give the most inert performance? I am thinking of using two 1/2" thick pieces of aluminum with a constrained layer damping polymer between them. It can be painted high gloss black at an auto body shop. Of course, it would be a lot easier to buy an arm board from VPI, but that is definitely "less fun." Any suggestions?