Conduction is the transfer of heat through direct contact between materials. Thermal energy moves through microscopic interactions between neighboring particles, generally from a hotter region toward a cooler one, without the material as a whole flowing from place to place.
In solids, especially metals, conduction occurs through vibrations of atoms and, in metals, the movement of mobile electrons. Metals are therefore usually good thermal conductors. Materials such as wood, foam, and air conduct heat much more slowly and are commonly used as insulators.
Conduction is one of the three main modes of heat transfer. Convection involves the bulk movement of fluids such as air or water, while radiation transfers energy through electromagnetic waves and does not require direct contact. In real situations, all three processes can occur together.
The rate of conduction depends on factors including the temperature difference, the material's thermal conductivity, the distance heat must travel, and the cross-sectional area. The SI unit of thermal conductivity is watts per metre-kelvin, written W/(m·K).