check out B-Quiet for various sound deadening/absorbing products.
http://www.b-quiet.com/vcomp.html
"Vcomp is a noise barrier composite consisting of a dense 1/8" vinyl based polymer barrier with a 1/4" thick foam decoupler. It has a total thickness of 3/8", weighs approximately 1 lb/sq. ft. "
I've used their dampeners before, they're great quality.