The ability of thermal materials, particularly those used for building and construction purposes, to moderate internal temperatures and to regulate heat release, and therefore to delay the time at which peak temperatures occur. It is the product of the mass and heat capacity of the material and has the SI units of J K⁻¹. A high thermal mass can store and later release large quantities of heat without a large temperature rise on the surface, whereas a low thermal mass can release its heat quickly. See thermal capacitance.