Apparently Dynomat blocks in sound waves though, thats the only difference. I think I would believe it but right now all I care about is getting the back of my trunk to stop rattling. The area where the keyhole is vibrates so bad...so I need to put some foam in between to stop it from moving. Anybody got any ideas on some thick, dense, all weather foam to put along the edge? I cant think of anything around the house.