conduction, heat

Flow of heat energy (see energy transfer) through a material without the movement of any part of the material itself (compare conduction, electrical). Heat energy is present in all materials in the form of the kinetic energy of their constituent vibrating particles, and may be conducted from one particle to the next in the form of this vibration.

Different materials conduct heat at different rates. This rate is called the thermal conductivity. A good conductor of heat, such as steel, will have a high thermal conductivity and a poor conductor of heat, such as air, will have a low thermal conductivity. In general, non-metals, such as wood or glass, are poor conductors of heat.

In the construction industry, the thermal conductivities of the materials to be installed need to be known. A low thermal conductivity indicates that a material is a poor conductor of heat and therefore a good insulator. For example, foam is used to insulate lofts, the air trapped in the foam making it a good insulator. Bricks used in outer walls have tiny air spaces, again allowing air to be trapped and making the bricks good insulators. Insulation can also be achieved with double-glazed windows, with the space between the two glass panes containing air or a vacuum.

In the case of metals, which are particularly good conductors of heat, the free electrons within the material transport heat around very quickly.