Thermal conductivity is defined as the amount of heat (in watts) transferred through 1 one square metre (m2) of an insulating material (or any other material) of a given thickness (in metres) due to a difference in temperature. The lower the thermal conductivity of the material the greater the material’s ability to resist heat transfer, and higher its thermal resistance (R-value).

How to calculate the R-value of EPS Expanded Polystyrene?

Typical thermal conductivity values for expanded polystyrene is 0.035 W/m∙K. This means, a 40mm thick EPS panel, will have an R-value of 0.04/0.035=1.14 m2/(W.K). Similarly, a 100mm thick EPS panel, will have an R-value of 0.1/0.035=2.85 m2/(W.K).