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My husband travels to lots of weird and wonderful places for his job and as such has lots of interesting travel products that he takes with him such as malaria strength insect repellent, mosquito nets and packets of these foil blankets. We then have access to the products as a family as he keeps all of these at home and we often take some of these blankets camping with us. Its not really what they are meant for, they are more an emergency item which is why my husband has them in his travel case. You often see them given out to runners after a marathon as they help them after the race to cool down properly and recover properly.
Camping is not my favourite thing to do, I can go for a weekend, that is about it but there something about sleeping on the floor in a cold, often damp wet tent that is just not fun. I hate being cold but these blankets are great at really keeping the heat in. These are not actually a blanket as we know it, they are not soft and comfortable and squishy, they are in fact a large section of foil which is fairly thin but has excellent heat retaining and cooling properties. I like to take these away because when they are new and all folded up they take up hardly any space which is much better than having to take lots of big blankets.
This blanket is silver on one side and gold on the other. For protection against the cold which is what we use these for you need to wear the blanket with the silver side towards the body as this aluminium metalled side reflects approximately 80% of body heat. These blankets are lovely and really do keep me nice and warm when I need an extra layer on cold nights in the tents. I tend to keep it on beneath my sleeping bag and then at some point during the night I usually take it off as it is quite warm but it provides the perfect start to a cold night. The instructions say you must never cover your face as this could be dangerous and I can see why.
If you did ever need to use this blanket for protection against the heat you would use it silver side up as sunbeams are reflected and so you are kept cool.
According to an article I read, they were,"First developed by NASA in 1964 for the US space program, the material consists of a thin sheet of plastic (often PET film) that is coated with a metallic reflecting agent, making it metallized polyethylene terephthalate (MPET), usually gold or silver in color, which reflects up to 97% of radiated heat.
We get these as part of a travel kit from my husbands work but I assume you can buy them online and in specialty outdoor stores.