Because I was getting tired of the road noise and engine noise in the passenger compartment, I used a cheap product called GTmat. .050" thick aluminum foil faced sticky rubber-like product that worked pretty well to limit the noise in the cockpit. I used a single layer for the most part on the firewall behind the seats and it did an OK job of quieting the engine droning (3.4 DOHC with custom exhaust). Less than $40 for 25 sq. ft. was enough to do the firewall, rear pillars, and doors. The only problem I have with it is the smell but that is going away with time....and an air freshener. I wouldn't pay the price for Dynamat....way way overpriced!
This stuff does have an odor but the asphalt stuff from homey depot stinks something terrible. The neighbor had the stuff on his roof and it stunk in my house. I can't imagine how bad it would be inside a little car!
[This message has been edited by SKIDMARK (edited 11-02-2013).]