I bought a roll of something that's 3/8" thick, foil faced, and meant as an acoustical and heat barrier for under carpets, internal firewalls, etc. It's 48"x24'. I bought the roll at J.C. Whitney for around $75 and used it for additional insulation on the fridge. BTW- I set a torch to it and it refuses to sustain combustion. All it does is get black until I remove the torch, then noting.
Jeff - WA6EQU
'06 Itasca Meridian 34H, CAT C7/350