Thermal conductivity definition

The effectiveness of a material as a thermal insulator can be expressed in terms of its thermal conductivity (TC). The energy transfer rate through a body is proportional to the temperature gradient across the body and its cross sectional area. In the limit of infinitesimal thickness and temperature difference, the fundamental law of heat conduction is:

Q = λAdT/dx


  • Q is the heat flow (W)
  • A is the cross-sectional area (m2)
  • dT/dx is the temperature/thickness gradient (K/m)
  • λ is defined as the thermal conductivity value (W/m. K)

Thermal conductivity λ

A substance with a large thermal conductivity value is a good conductor of heat; one with a small thermal conductivity value is a poor heat conductor i.e. a good insulator. Hence, knowledge of the thermal conductivity value (units W/m. K) allows quantitative comparisons to be made between the thermal insulation efficiencies of different materials. The most effective insulation will have very low thermal conductivity values. Our graphs show that Microtherm® has very low thermal conductivity values for a wide range of temperatures - in contrast with all the other material classes presented.

Thermal conductivity definition  |  Related terms  |  Measurement of Thermal conductivity