3.4 - I used this stuff from lowes in the back of my tahoe to help with exhaust noise. I put two layers down from the rear seats back and it really helped alot. I have had it there for about a year and its still sticking like day one.
alot of perople uses the peel & seal from home depot then use a layer of reflectix for heat. Some love it cause its cheap and works pretty good and some love the exp name brand stuff. Its up to you.