Thermal conductivity can be explained as the amount of heat that is transferred over a certain amount of time due to a temperature change.
This is an intensive, or bulk, property, meaning that the thermal conductivity of a material stays the same no matter the size or amount of the material.
All materials have some level of thermal conductivity. Air and similar gases typically have low levels, while electrical insulators, like diamond, have high levels.
Thermal conductivity is measured using a number of different techniques. Transient techniques measure temperature as a material is heating up, while steady-state measurement is used when temperature is not fluctuating.
A number of different industries, like building insulation in construction, rely on knowing the thermal conductivity of materials.
By Mark Orwell, eHow Contributor