Reflective coating on emergency blankets reflects your own body heat to keep you warm.
So if this technology is designed to reflect heat, how will it help you when you're stranded on a freezing mountain? The clever engineers at NASA may have developed the material used in emergency blankets as a means of insulating against heat and preventing their precious equipment from being destroyed in space, but they quickly realized that they could also use the technology to retain heat, just by flipping it over.
If you find yourself in an emergency situation where you're losing body heat faster than it's being generated-like if you're lost on a long hike, fallen through ice, or just finished a very long and hard trail run-you're at risk for hypothermia. If you can't get indoors right away, you can grab an emergency blanket from your first aid kit and wrap it around yourself to conserve and increase your own body heat. Instead of facing the foil side toward the sun to block out the heat, you turn it toward your body so that it reflects your body heat back to you.
Conversely, if you're lost on a very hot hike with no shade, you can turn the foil side of the emergency blanket outward to reflect the sun's heat.