Types of Foam Board
Extruded Expanded Polystyrene Foam Board
Extruded expanded polystyrene (XEPS) is a closed-cell foam insulation. To make it, the polystyrene pellets are mixed with various chemicals to liquefy them. A blowing agent is then injected into the mixture, forming gas bubbles. The foaming, thick liquid is then forced through a shaping die. When cooled, the panel is cut as required. Foam densities are typically 1.5 pounds per cubic foot (24 kilograms per cubic meter).
The R-value depends upon the density of the material and is generally about R-5 per inch. It’s also much more consistent in density, making it better suited for use on roofs or for wall panels. Extruded polystyrene also has excellent resistance to moisture absorption.