The stuff Home Despot sells something that's been reviewed on here a ton of times, did a quick search and found THIS INFO
I found something on eBay called "Fatmat" which is a similar butyl rubber, foil backed self adhesive material. The difference I've seen so far is that you get about 35 sq ft of Dynamat for around $250.00, but you get about 100 sq ft of Fatmat for about $40.00 (as I recall). I still have to find out how much each product weighs per sq ft, as that would tell me if Fatmat is the same thickness.
Eastwood is also selling a second name brand (medium priced), as well as their own brand (lower priced). I didn't keep the catalog, but you can check their website, prices in general seem to be coming down as competition increases.
The Jalopy Journal
