Most solids expand when heated.
The reason for this is that this gives atoms more room to bounce about with the large amount of kinetic energy they have at high temperatures. Typical numbers for range from for hard solids to organic liquids. Mostly thermal expansion is a nuisance for engineers and there is much interest in creating solids with little or no thermal expansion. I am actually working on understanding a new interesting and promising material in this respect which has a negative coefficient of thermal expansion that is it contracts with increasing temperature. Mixing some of such a material with other materials which expand upon heating it may be possible to create solids with little or no thermal expansion.