to light weight open cell foam on top of that. Foam also on the wall behind the seats. Rats nest and polyfill in all of the deep open cavities. Everything is hidden under the interior. I measured before and after with my sound meter at idle and at 65 on the freeway. In both cases it dropped 5-6 db. Note each 3 db drop is about 1/2 of the sound magnitude. It was significant. I have a full 2.5 inch turbo back SZ exhaust with X pipe, flex pipe and resonators and i can have a conversation at freeway speed without having to speak up. The only downside is i added about 30lbs of stuff. But i did remove the spare tire due to BBK, so not as bad of a net gain.
