How a thin sheet sends body heat back
A person loses warmth in several ways. One is radiation: the body emits invisible infrared energy, much as a warm object gives off heat that you can feel nearby. A polished metal layer reflects much of that radiation instead of absorbing it and sending it onward. Wrapped around someone, the reflective surface can redirect some of the person’s radiated heat back toward them.
The aluminum layer is extremely thin, so the blanket stays light and flexible. The plastic film beneath it provides a tough backing; stretching the polyethylene terephthalate (PET) aligns its molecules, helping the film hold together as a very thin sheet. The metal coating supplies the reflective surface.
What the blanket can—and cannot—do
The blanket does not produce heat. It helps conserve warmth already coming from the body, and its effectiveness depends on how it is used. Covering someone loosely leaves gaps where warm air can escape; wrapping them helps limit that loss. The sheet also blocks wind and can keep rain from directly wetting clothing, which matters because moving air and wet fabric can carry heat away quickly.
But a thin film is not a thick insulating layer. If it is pressed against a cold surface, heat can still pass through by direct contact, and the blanket cannot replace dry clothing or shelter. Its advantage is a different one: a very small amount of material can reduce heat loss without the bulk of a conventional blanket. That is why a folded reflective sheet can be carried as emergency gear, then opened to cover a person when warmth matters.
