Interior Insulation

It depends on what you're trying to accomplish. The gentleman above used it in his truck, which is really smart beause those old trucks were about 3x louder inside than cars. Me personally, I just bought carpet with the thick jute backing on it and installed it that way. It's quiet enough to where I'm not bothered by road noise, but loud enough to where I can hear any strange engine, suspension or rear end noises. You don't want to be too insulated because you could possibly be driving around with a problem and not know about it for a while.