Thermal expansion is the tendency of matter to change in volume in response to a change in temperature, through heat transfer. The degree of expansion divided by the change in temperature is called the material's coefficient of thermal expansion and generally varies with temperature. Unlike gases or liquids, solid materials tend to keep their shape when undergoing thermal expansion. Thermal expansion generally decreases with increasing bond energy, which also has an effect on the melting point of solids, so, high melting point materials are more likely to have lower thermal expansion. In general, liquids expand slightly more than solids. The thermal expansion of glasses is higher compared to that of crystals.