Winter coats contain pockets of air that keep heat from moving away from your body. This is an example of
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Answer:
There are three ways to transfer heat from one place to another: convection (via moving air), conduction (via direct contact), and radiation (via electromagnetic rays, like an IR heat lamp). A jacket works by slowing down one or more of these heat loss paths.
A windbreaker, for instance, prevents the cold wind from blowing away the warmer air close to your body, so it cuts down mainly on convective losses.
One of those puffy down jackets that you see people wear in cold mountain areas also adds insulation. Insulation is pretty much anything that transfers heat slowly, and heat transfer is slowed when it has to change materials, like transferring from air into another substance, so, generally speaking, the more layers you have the better insulation you’ll create. This minimizes conductive losses.
An example of a material made especially to block radiative heat loss is an emergency heat blanket, sometimes called a “space blanket”. These are made of specially coated Mylar, and work by reflecting a large percentage of infrared radiation.
The best kind of jacket would effectively address all of these kinds of heat loss.