The Complete Handbook of Emergency Blankets

Chapter 1: Understanding Emergency Blankets

The emergency blanket - also called a space blanket, thermal blanket, or mylar blanket - is one of the most common pieces of survival equipment in the world, and one of the least understood. It is a thin sheet of plastic film coated with a metallic layer, typically aluminum, designed to reflect radiant heat back toward the person wrapped in it. In its standard form, it measures roughly 52 by 84 inches (132 by 213 centimeters), weighs between 40 and 80 grams, and folds down to the size of a pack of cards. That simplicity is deceptive. The difference between a blanket that keeps a stranded motorist alive through a cold night and one that gives that same motorist a false sense of security while they develop hypothermia is not a matter of price or brand. It is a matter of physics, material quality, and correct use.

The operating principle of an emergency blanket rests on three separate mechanisms of heat transfer: radiation, conduction, and convection. A human body loses heat through all three simultaneously, but the proportions vary dramatically depending on the environment. Radiation - the direct emission of infrared energy from a warm surface to a colder surface - accounts for approximately 40 to 50 percent of heat loss in a calm indoor environment at room temperature. In an open outdoor environment at night, that percentage can climb higher, especially when the sky is clear and there is no cloud cover to reflect