A emergency blanket (depending on the function, also known as a Mylar blanket, first aid blanket, safety blanket, thermal blanket, weather blanket, heat sheet, or commonly referred to as shock blankets) is an especially low-weight, low-bulk blanket made of heat-reflective thin plastic sheeting. They are used on the exterior surfaces of spacecraft for thermal control, as well as by people. Their design reduces the heat loss in a person's body, which would otherwise occur due to thermal radiation, water evaporation, or convection. Their compact size before unfurling and light weight makes them ideal when space or weight are at a premium. They may be included in first aid kits and also in camping equipment. Lost campers and hikers have an additional possible benefit: the metallic surface appearance flashes in the sun, allowing use as an improvised distress beacon for searchers and also as a method of signalling over long distances to other people on the same route as the person who owns the blanket.