Solids mostly expand in response to heating and contract on cooling. This response to temperature change is expressed as its coefficient of thermal expansion.

The coefficient of thermal expansion is used:

• in linear thermal expansion
• in area thermal expansion
• in volumetric thermal expansion

These characteristics are closely related. The volumetric thermal expansion coefficient can be measured for all substances of condensed matter (liquids and solid state). The linear thermal expansion can only be measured in the solid state and is common in engineering applications.