Today i have made 2 pot cozy's. I take no credit for the design as i have seen a similar one, i think it was on Colin Ibbotson's site.
I first made one from roofing insulation, similar to the type sold on www.backpackinglight.co.uk and AntiGravity Gear but i couldn't find a good enough tape to hold it all together. I tried the usual duct tape and carpet tapes but they fell apart very quickly. I tried exhaust tape but again it didn't last long.
I have made the cozy from an old karrimat and glued the pieces together with araldite. They work a treat keeping your dehydrated food warm for ages, are very light and don't fall apart.