I think what you maybe looking for is what is called two part foam ( expanding urethane foam )
It can expand at various rates to give you different densities of foam. Here is a link to Smooth On to get you started. Check around for other suppliers and do a search here in the forum.
Another note, its not cheap.
No matter where you go, there you are.
Last edited by Bone Dancer; 04-24-2012 at 10:41 PM.
Reason: two part foam, expanding urethane foam