Here's a picture of what's under my carpets, tunnel and rear wells. Lead, with foam on both sides. Just cut, laid, formed and fit in place, not glued. Tunnel carpet, just laid in, not glued (not fully in place in picture). Soaks up sound and vibration. Great stuff, if not a touch heavy. Felt pieces on top in front to flatten floor.
Difficulty posting pictures? Banish the thought!