The reflective coating on the emergency blanket reflects your own body heat back to you to keep you warm.
So if this technology is designed to transfer heat, how can it help you when you're stranded on a frozen mountain? NASA's clever engineers may have developed the material used in emergency blankets as a means of retaining heat and preventing their precious equipment from being destroyed in space, but they soon realized they could also use the technology to Keep the heat on, just by twisting things around.
If you find yourself in an emergency situation where you're losing body temperature faster than you can produce it - say you've gotten lost on a long hike, fallen on ice or just completed a very long and strenuous trail run - you have Risk of hypothermia. If you are unable to get indoors right away, you can grab an emergency blanket from your first aid kit and wrap it around yourself to preserve and increase your own body temperature. Instead of having one side of the foil facing the sun to block heat, you have it facing your own body to reflect your body heat back to you.
Conversely, if you find yourself lost without shade on a hot hike, you can use an emergency blanket with the foil facing outward to reflect the sun's heat.