Thermal conductivity
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The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k', λ, or κ.
General
Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal conductivity. Likewise, homogeneous materials transmit heat better than heterogeneous ones. For instance, metals typically have high thermal conductivity and are very efficient at conducting heat, while the opposite is true for insulating materials like styrofoam. Correspondingly, materials of high thermal conductivity (like metals) are widely used in heat sink applications and materials of low thermal conductivity (like asbestos) are used as thermal insulation. The reciprocal of thermal conductivity is called thermal resistivity.
The thermal conductivities of common substances span at least four orders of magnitude. Gases generally have low thermal conductivity, and pure metals have high thermal conductivity. For example, under standard conditions the thermal conductivity of copper is over 10000 times that of air.
