I decided I would do the test I mentioned in my initial post when I found, for a quarter at a garage sale, a more or less "typical" mylar survival blanket (it was the brand that says "Made in Israel"). For a moment or two, I kind of had a little fun with it in the wind. I later discovered that this was, by far, the best use of it. Then I decided to lay it out on my grass lawn and try to wrap up in it. The size of the thing was all wrong. When I tried to use it sleeping-bag style, to cover myself full length, it wouldn't go all the way around my body. When I used it the other way, it wouldn't cover my head or my feet. And neither way would work when I was sitting cross legged style on the ground. No coverage at all was possible under me. By this stage, the thing had started to tear and become completely useless. I did notice an immediate sensation of warmth, however, when I sort of got the thing semi-wrapped around me. This lasted maybe a half a minute before the wind started blowing the thing open here and there.

I'm going to get a few of those AMK Heatsheets to try, the ones sized for 2 people. I think it must sort of be like the freeze dried meals. If you buy one suitable for 2, one person might get full. At any rate, the AMK ones are definitely supposed to be re-useable, heavier, quieter, and they have survival tips printed on them to at least keep you entertained while you're freezing to death.