Picture the end of a marathon. The knackered survivors are being handed the race sponsor's products and... wrapped in tin-foil? They are given a silvery, shiny sheet, and they sit exhausted by the side of the road, wearing it like a space-granny's shawl. This is a space blanket.
A space blanket is a sheet of plastic, perhaps a polyester film such as Mylar, that has been coated with metallic particles. They can be made by spraying aluminium vapour onto any flexible sheet. The resulting blanket is highly reflective of light, and therefore unsurprisingly, it also reflects heat- as much as 90%.
That's why they're so useful for long-distance runners. After a lot of strenuous exercise, wearing light, breathable clothes, they stop. They are soaked through with sweat, and they're outside. It's a recipe for hypothermia. Any wind will whip heat away from exposed skin, and the sweat will evaporate, drawing precious body heat away into the ether. Neither phenomenon mattered during the run, when the body was expending energy and generally getting hot.
A space blanket does a good job of combating heat loss. Like other blankets, they trap air near the skin, creating an insulating layer. But unlike non-space blankets, they're totally impermeable to the wind; so they also trap evaporated sweat, raising the humidity near the skin and reducing further evaporation. Crucially, they reflect almost all radiated heat back to the body. A marathon might see hundreds of amateur athletes finishing every few minutes. A space blanket can be made for a few pennies, weighs a few ounces, and is stored very compactly. Imagine the expense of stocking thousands of heavy wool blankets.
Their proven heat retention and ease of storage also makes them ideal for camping and first-aid kits. In particular, victims of shock can benefit from being kept warm. They offer improved visibility from a distance, at least during daylight, and keep the shroudee nice and dry.
Suppliers also happily sell loft insulation wrapped in space blankets. An additional benefit here may be to keep the irritant insulation materials away from the DIYer's delicate hands.
Space blankets are a direct result of NASA's research programmes. They were designed to protect astronauts and advanced electronics from radiation and extreme cold on the Apollo missions.
They are still made for the civilian market by MPI, the company who first supplied them to NASA in 1964. I like to think the name "Space Blanket" has stuck not because of their association with Cape Canaveral's Propellerheads, but because they're shiny. I think for most people:
Many online emporia and camping shops sell space blankets. In large quantities a 7 × 5 feet blanket costs under a pound. They are also known as Marathon Recovery Capes and Emergency Blankets.
If space blankets are the space-age heating product; then perhaps laser cooling is their space age opposite.