Material properties spanning six orders of magnitude
Thermal conductivity measures how easily heat flows through a material under a temperature gradient. Diamond leads at over 1000 W/m-K due to its rigid crystal structure and strong atomic bonds. Metals like copper and aluminum range from 200-400 W/m-K. Common solids like stone, concrete, and glass are 10-100 times lower. Water is 0.6 W/m-K, and air is 0.026 W/m-K. This spread means thermal behavior is dominated by the material choice.
Conductivity depends on temperature. Metals decrease with rising temperature because atomic vibrations scatter heat-carrying electrons. Gases increase with temperature, following kinetic theory. These temperature sensitivities must be accounted for in high-precision thermal calculations.
Using material conductivity in thermal design
For rapid heat transfer, engineers choose high-conductivity paths: copper for heat sinks, aluminum for radiators. For insulation, they use low-conductivity materials: foam, fiberglass, or air gaps. The rate of heat flow by conduction is proportional to conductivity, area, and temperature difference, and inversely proportional to thickness.
Composite structures combine materials strategically. A semiconductor on a copper heat sink achieves fast removal because heat flows through the high-conductivity copper quickly, then spreads over a large surface area for convection. Thermal interface materials bridge small gaps that would otherwise trap air (a poor conductor) and obstruct the path.