Well, I'm not a fan of the thin mylar ones- I spent a very, very cold night that turned into a clammy and cold one inside one of those. I'd rather use a poncho with liner on me, and then the mylar over the frame work- it's shininess might help it be found in a night search (I know, not likely, but it's worth a shot), reflects the sun somewhat during the day, and casts some of your firelight back if you are working on something after sundown. <br><br>But around the body, I've never really found themto be much more effective than a plastic sheet of the same thickness. But I also sweat a lot in my sleep, so......