First, let me get this straight, this is not one of those flimsy tin foil emergency blankets. What is it? An all-weather space blanket is a half tarp and a half emergency blanket. On one side it is a tarp that comes in an array of colors. On the other side is a shiny foil – kind of like a durable emergency blanket. Just like the emergency blankets these provide you 90% of your body heat back and are rain and wind resistant.
If you take care of them they will last for many years. I have two, and both are over 15 years old. I keep them in a nylon bag which also includes my rain poncho. Whenever I go on a road trip, camping, backpacking, etc I take this bag with me. When I sleep under the stars, which is often, I place one under me and one over me. Experience has taught me there will be dew trapped between you and the tarp. Make sure you dry the tarp and your bag before putting them away to prevent mildew.
You can see my green one in this picture. Also, they are available from Amazon for around $15.