What does thermal conductivity measure?

Thermal conductivity is a fundamental property of materials that quantifies their ability to conduct heat. This means that it measures how easily heat energy can pass through a material when there is a temperature difference across it. A high thermal conductivity indicates that the material allows heat to flow readily, making it an excellent conductor of heat.

In practical applications, knowing the thermal conductivity of materials helps engineers and designers choose appropriate materials for insulation, heating, and cooling applications. For example, metals typically have high thermal conductivity, while insulative materials like fiberglass or foam have low thermal conductivity.

The other options relate to different thermal properties: while one mentions heat retention, which is more about a material's thermal mass and specific heat capacity, another refers to thermal expansion resistance, which is connected to a material's structural characteristics rather than its heat conduction ability. Meanwhile, the efficiency of a heat pump involves thermodynamic principles instead of a direct measurement of how heat is conducted by a material. Thus, the focus on heat conduction makes the correct choice clear.