Thermal conductivity measures how well a material conducts heat, in W/(m·K). The higher the value, the faster heat moves through the material under the same conditions. This note explains the definition, lists reference values for common materials, and works through an example that converts conductivity into an actual heat flow.

Definition and influencing factors

Under steady-state conditions, take a 1 m thick layer of material with a 1 K difference between its two faces (1 degree Celsius works as well). The heat passing through 1 m² of area in one second is the material's thermal conductivity. Beyond the type of material, the value depends on microstructure and filler content, so in engineering it is normally determined by test. Many test methods exist, each with its own range, accuracy and sample-size requirements, and the same sample can give noticeably different results from different methods.

Reference values

Worked example

At steady state, heat flow Q = λ·A·ΔT / d. For solid silicone (λ = 0.35) with thickness d = 2 mm = 0.002 m, area A = 0.01 m² and a temperature difference ΔT = 10 K, Q = 0.35 × 0.01 × 10 ÷ 0.002 = 17.5 W. Under the same conditions copper conducts roughly 1,100 times as much heat as silicone, which shows how far apart metals and polymers are in heat transfer.