Since I have this big roll of marvelseal 470, I've been trying to figure out how to use it. Thanks to MacEntyre, I now know what to do with it!
There's not a whole lot of info on this material except in sealing archival materials and such with it. So I got out a clothes iron and had at it to try and seal the edges. It works! So now I can make water bags, cozies, storage bags and I don't know what else. It makes a great vapor barrier and I understand MacEntyre is using it for all manner of things where you don't want sweat to go.
Here's some pics of the process. You can get marvelseal on the web and also museums have it for storing delicate wood frames, books and such. I now have a piece I carry to sit on out in the woods. I'll have a nice pot cozy later this evening.
I don't believe it would work in a hammock - maybe someone familiar with vapor barriers can chime in with some other uses.