They're called Space Blankets because the material was first used in laminate space suits. One layer of the material will optimally reflect 90% of base body heat. The second layer reflects 90% of the escaping 10% and so on- in the controlled hermetic environment of a space vehicle. It makes you want to reach for a Hudson's Bay 5 striper and teddybear doesn't it <img src="/images/graemlins/grin.gif" alt="" /> The unit's strength is in portability. We are more likely to 'warm' to the idea of slipping a sealed unit into a pocket than that big old Hudson. The weakness is the simplistic hype from pop culture showing a avalanche victim deploying one and start working on their tan. They come into their own building emergency shelters. Draping one over your framework makes an excellent reflector to retain heat from a fire and bringing a little order to all the leaves, bark slabs, spiders, rattlesnakes,coyotes and pinecones you start piling on top. Survival illustrations always show an elegant geometrically perfect shelter. Mine look like a Foster's Freeze jumbo vanilla in 100 degree weather <img src="/images/graemlins/mad.gif" alt="" />