I used reflectix as an under pad last winter. It felt as though it would extend the use of my, then, old walmart closed cell. I would give you a peice, but the roll I bought made a few cozys and one pad for me, Then my camping buddy got hold of it and went to town making stuff. I think the roll cost 14.00 at home depot. It is light and water proof. Now bear in mind that it was in an OR advanced bivy, but I took my 20 bag to 10 degrees last year (wearing every stitch of clothes I had) with the aid of reflectix. And then continued to use it through last February. I could go into more detail, but the stuff is cheap enough and light enough to warrant your own tests. And it does make some really good cozy material.