Properties of soapstone

Thermal conductivity: 6.4 W/mK

Specific heat capacity: 0.98 J/gK

Density: 2,980 kg/m³

Flexural strength along the grain: 16.8 MN/m²

Flexural strength perpendicular to the grain: 15.7 MN/m²


Thermal conductivity

The fact that soapstone has a better thermal conductivity compared to other materials is a consequence of its dense structure and mineral composition. This characteristic enables balanced and rapid warming throughout the soapstone structure.

Volumetric heat capacity

Volumetric heat capacity is the amount of heat energy a material is able to bind both per temperature unit and per weight or density unit.

The specific heat capacity of soapstone is about 1 J/gK and its density about 3 g/cm³, making its volumetric heat capacity 3 J/cm³K. The mineral magnesite has good thermal conductivity and heat capacity. The specific heat capacity for natural stone is usually 0.84 J/gK, making the value for soapstone about 20% greater than average.


Many people have a mistaken impression of how compact soapstone is, thinking that a soft stone must also be porous. It can be concluded from soapstone’s high density that it does not have a porous structure. Soapstone was created in high temperatures and under great pressure over a couple of hundred million years. Moisture clings only to the surface of soapstone and is unable to force its way inside, even under pressure. In tests conducted by the VTT Technical Research Centre of Finland (research report number 174/80/BET), a result of just 0.08% was obtained for the effective porosity of soapstone. The porosity of good building stone can be 0-30%. Soapstone is structurally dense.

If moisture gets inside natural stone, it weakens the strength properties of almost all types of stone. If a stone gets wet unevenly, it can bend. Soapstone’s high density prevents moisture and chemicals from entering the stone, and it is therefore not prone to the previously-mentioned problems.

Flexural strength

The flexural strengths of soapstone are over 60% of its compression strength. This is a very rare phenomenon among stones, as the flexural strength of natural stone is usually about 5-10% of its compression strength.

Chemical durability and purity

Soapstone has excellent chemical durability - not even strong acids can damage it. Soapstone is also pure. It fulfils the requirements set down in Section 16 of Finland’s Food Act and Decree.