Extruded polystyrene foam (XPS) consists of closed cells, offers improved surface roughness and higher stiffness and reduced thermal conductivity. The density range is about 28–45 kg/m3.
Because of the extrusion manufacturing process, XPS does not require facers to maintain its thermal or physical property performance. Thermal resistivity is usually about 35 m·K/W (or R-5 per inch in American customary units) but can range between 29 and 39 m·K/W depending on bearing/density. Thermal conductivity varies between 0.029 and 0.039 W/(m·K) depending on bearing strength/density and the average value is ~0.035 W/(m·K).
Water vapour diffusion resistance (μ) of XPS is around 80-250 and so makes it more suitable to wetter environments than EPS.
Extruded Polystyrene (XPS) is manufactured to TIASA standards with fire classification in accordance with SANS 428.