FOAMULAR® 604 Extruded Polystyrene (XPS) Rigid Foam Insulations are specially designed for use in Protected Roof Membrane Assemblies (PRMA), where the insulation is placed directly over the membrane. FOAMULAR® XPS Insulation is produced by Owens Corning's patented HydroVac process technology under conditions of strict quality control. The compressive strength of FOAMULAR® XPS Insulation provides the integrity needed for long-term roof performance.