Therma Wall The GPS Therma Wall is comprised of 1 inch EPS bonded to ½ inch drywall. It has a total insulation value of R5-5. It is ideal for insulating external basement walls. Insulation thickness can be increased to gain a greater R-value as required. It can be finished and decorated as plasterboard. Therma-Wall can be fixed to most types of sound walls or ceilings. It is easy to cut and easy to install. Therma Wall achieves Class 1 surface spread of flame. No framing or special tools required. No vapor barrier required. High resistance to water vapor passage. Permanent low thermal conductivity. Available in 4’X8’ and 4’x10’ panels. Standard thickness 1 1/2” = R5.5.f