Properties of soapstone

Specific heat capacity c is the energy required to raise the temperature of 1 kilogram of a building material by 1 kelvin. It is a material constant with the unit J/(kg·K). Its value can depend on temperature; for standard calculations it is usually assumed to be constant. The greater the specific heat capacity of a building material, the more slowly it heats up for the same mass and the same heat output, and the better it buffers temperature peaks. The actual buffering effect also depends on the mass, the thermal conductivity and the accessible surface area of the component. It therefore has a direct influence on comfort and the climate in a room.

The table above raises the question of what advantage soapstone has over, for example, concrete and pumice. Both have a similar or even greater specific heat capacity. The answer lies in the ability to store heat per unit of volume. For the same volume and the same change in temperature, soapstone can store more heat. The heat storage coefficient S is the product of the specific heat capacity and the density of the material. Soapstone has a higher density than, for example, standard concrete and pumice, and can therefore absorb more heat for the same volume.

Thermal conductivity λ (lambda) indicates the heat flow passing through a layer of material 1 m² in area and 1 m thick at a temperature difference of 1 kelvin. The unit is W/(mK). The smaller λ, the better the insulating capacity of a building material. The higher the thermal conductivity, the faster the material releases heat into the room.