In order to get the maximum enjoyment from your expensive new car audio system, you’re going to need some auto sound deadening material. This material is installed against outer body sheet metal under the door and carpet, and behind side panels to cut down on transmitted vibrations and sound. This product is a very dense form of urethane impregnated acoustic foam. The foam is designed as such to block the transmission of sound. When installed against body panels and under the carpet, the sound deadening material absorbs vibrations generated by vehicle components and damps them. Properly installed, sound deadening material can almost completely isolate your car’s interior from the outside world.
For more info, see 3 Facts about Car Speakers