Extruded polystyrene foam
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.
Extruded polystyrene material is also used in crafts and model building, in particular architectural models. Because of the extrusion manufacturing process, XPS does not require facers to maintain its thermal or physical property performance. Thus, it makes a more uniform substitute for corrugated cardboard. 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.