Those Mylar-coated emergency blankets certainly don’t look very warm. How on earth can something no thicker than a trash bag save your life? Well, though the aluminum coating on these blankets is very thin, it is thermal-reflective. In other words, it can redirect infrared energy, which means that it reflects heat. When you are getting cold due to shock or exposure, it’s because the heat you were radiating is lost to the air and not replaced. With a space blanket wrapped around you, however, the moisture in your clothes won’t evaporate (which causes cooling) and you won’t lose as much heat to the air moving around you (limiting convective heat loss). So you will stay warm when you’re wrapped up in this sheet that looks like tin foil. And since these lifesaving blankets pack down so small and are so cheap, there’s no reason to run around in the bush without carrying a few of them.