Thermal conductivity is defined as the amount of heat (in watts) transferred through 1 one square metre (m2) of a material of 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).

What is thermal conductivity 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 R value of 0.04/0.035=1.14 m2/(W.K). Similarly, a 100mm thick EPS panel, will have R value of 0.1/0.035=2.85 m2/(W.K).