tar based material that usually has a sticky side to it like a sticker that you press on to outer/inner door panels or body paneling that absorb the road noise or rattling caused by deep loud bass. The worst bass rattling usually heard comes from the license plate. But once you put in a good deal of sound deadening material, you don't have to crank up your volumes so much
I'd go for brands like Hushmat or Second Skin which are cheaper than Dynamat. Dynamat is more widely picked because it's available at most car audio places, but it's very expensive even from 3rd party online vendors. Some people also use Peel N Seal from places like Home Depot which do the same thing but is a lot cheaper. I'm not sure though if Peel N Seal can withstand the extreme temperatures like Second Skin, Dynamat or Hushmat or Fatmat.
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