|How can heat be trapped? — PR, Brooklyn, NY
You can prevent heat from moving about with the help of insulation. The three principal mechanisms of heat transfer are conduction (the passage of heat through a stationary material), convection (the passage of heat in a moving fluid), and radiation (the passage of heat as electromagnetic waves or light). Good insulation doesn't conduct heat well, doesn't support convection, and blocks radiation. Wool is a good example: its hair and trapped air don't conduct heat well, the trapped air can't really undergo convection well, and thermal radiation can't travel through the wool along a straight path. As a result, wearing a wool sweater keeps you from losing heat quickly—you stay warm. Wool has the added benefit of carrying water away from your skin.