Extruded Polystyrene (XPS)

Another board insulation is made of extruded polystyrene (XPS) and often referred to as foamboard. XPS is a homogeneous product consisting of fine, closed cells containing a mixture of air and an insulating gas also used in other industries as a refrigerant. Available brands of extruded polystyrene are easily recognized by their colors: blue, pink, green, or yellow.

XPS is often referred to by one of its proprietary names, Styrofoam. Styrofoam extruded polystyrene insulation was devel­oped originally by the Dow Chemical Company in the early 1940s as a flotation material in liferafts and lifeboats.

XPS is manufactured by pushing freshly expanded foam through an extrusion die. A number of edge configurations are available, some straight and some with a profile designed to interlock to ensure a continuous thermal break and help to seal the joints between the panels.

XPS is used for insulating foundations and concrete slabs, for residing underlayments, and for exterior wall sheathing, for pro­tected membrane roof applications, and as the insulation for struc­tural insulating panels (SIPs) and insulating concrete forms (ICFs) (see Chap. 15). It is also installed either on the interior or exterior where space is limited such as cathedral ceilings, flat roofs, etc. (Fig. 11.5).