I know reflectex is a popular choice for MYO cozy projects, but we have really been enjoying these cozyies made from reflective coated closed cell foam (cut from an ordinary sleeping mat).
This is a set of well travelled cozies assembled using rip-proof and heat resistant plumbers tape. We find they keep the food better insulated than the bubble-wrap style cozies, and also protect the pot when it's in your pack. I originally tried making them with the reflective side to the inside, but found they weren't very robust like this. The relective coating is tougher than the closed cell foam. In an ideal world, I would use closed cell foam with reflective coatings on both sides, if anyone knows where to find some...