Keeping sound and heat out are two different animals. A foil backed deadener will help with the heat and some sound. I haven't used "fat mat" but it sounds like it's a foil backed deadener right? Something like dynamat extreme, hush mat, brown bread, etc will work for keeping vibrations down, heat out and some road noise. I've switched over to RAAM mat, it's an internet based company so you won't see it in summit etc, but it's good stuff, sticks like crazy and goes on easy....and the price is right, much cheaper than dynamat extreme. I just did a whole interior of a 37' Ford and can't imagine how long it would have taken with some of the deadener we used to use, the newer butyl based deadener (RAAM, Dyna extreme etc) really go on easy. For road noise/sound absorbtion I'd suggest a layer of foam or one of the foam based products dynamat or Cascade offer on top of your foil deadener, the floor, roof and firewall are the big areas to concentrate this stuff. Even an extra layer of carpet padding on the floor can help alot with road noise. It gets expensive but if your serious about getting it quiet cascade and I think dynamat have foam products with a layer of lead, the foam absorbs the noise, the lead actually will keep it out and reflect it (which everyone think the foil products are doing, they don't, they add mass to stop vibrations). Sorry for the ramble...but I deal with this often
Hope it helps.
Brian Hobaugh SCCA National Tour June 2014
First Hemi 'Cuda Convertible Ever Built
Short clips: Goodguys Pleasanton autocross and pit videos
Sound deadening help
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