A product which has been heavily promoted for a number of years is an aluminized plastic foil designed to reflect 80% of body heat. However, a large body of experience points to the following: 1. A minimal amount of heat is radiated by a clothed body. This can easily be demonstrated with a thermocamera. 2. The plastic foils is impermeable to both water and water vapour. Thus condensation is formed on the blanket's interior. This virtually eliminates the reflective properties of the aluminum foil, often after only 15-20 minutes. 3. The blanket usually works best when the wind velocity is less than 9 m/s, otherwise the wind tears it into pieces. The greater the wind velocity and amount of clothing worn, the less the effect of the blanket. 4. Water accumulation on the clothing inside the blanket rapidly conducts heat from the skin. The blanket and the aluminum then take over and conduct heat 9,300 times faster than air. 5. It is supposed to reflect radar waves. Theoretically yes, but practical tests made in lifeboats at sea have showed that it gives no help. 6. The plastic film is inflammable.