I have maybe ten of the cheapo emergency blankets, plus a 2 person HeatSheets blanket and the AMK HeatSheets bivy bag. So far I haven't tried the latter but I've tested the former and found them somewhat lacking. On the plus side, they do warm you up pretty effectively (although I haven't tested them yet in very cold conditions). But the kind I have (relatively sucky EverDixies I got from Amazon) really aren't sized and shaped the best. They're very noisy and extremely thin. They don't seem to tear all that easily, though. In virtually every instance I would have the blanket with me I'd also have some duct tape, so I figure I'd use tape form a bag or at least seal it up. In my Maxpedition water bottle kit I keep my Ritter/AMK PSP plus one blanket and a cheap poncho. I've tucked extra fire-making gear in the pouch and have a Mora with some paracord around the sheath. Out hiking this probably represents the least gear I would generally carry. Ideally I'll have a couple of the blankets along. I plan to stash a few of them in my vehicle for winter travel, too.

Eventually I'll try out the HeatSheets, too. Frugality has prevented me from doing so up til now as they're five times the price of the cheapo blankets, but obviously it's better to know what you're dealing with before you have to use them. If they're as good as I hear it will be money well spent. I have the Bivy style set up as a subscription on Amazon.com- every month they'll send me one and I get a discount and free shipping. This way they end up costing only $12 each, quite a savings. Well worth it if they actually save your life someday!