We use a product called Bonded Logic heat/sound insulation on the cars we restore at my shop. It's sort of like the jute padding on the underside of auto carpet kits with a foil backing on one side. About 3/8" thick. We use Dap Landau top and trim adhesive to apply it , but I've done inside of doors and other hard to reach areas with 3M 8088 spray adhesive.
Helps with sound and heat.
Kinda ashamed to say we get it from JC Whitney. We buy it in 4'x 48' rolls, but it's available in smaller quanitities
