Description: FOAMULAR® 404 & 404 RB extruded polystyrene insulations are specially designed for use in Protected Roof Membrane Assemblies (PRMA), where the insulation is placed directly over the ...

Rigid foam is the best insulation for rim joists. We chose 2-in.-thick (R-10) "extruded polystyrene." Don’t use "expanded polystyrene," which is a less effective air and moisture barrier.