Rigid Foam
Rigid foam refers to a family of board insulation products: EPS (expanded polystyrene, white "beadboard"), XPS (extruded polystyrene, often pink or blue), and polyiso (polyisocyanurate, foil-faced). Rigid foam is the standard material for continuous exterior insulation, sub-slab insulation, and basement walls. R-values run R-3.6 per inch (EPS) to R-6.5 per inch (polyiso fresh, derating to R-5 in cold weather). Embodied carbon, blowing agents, and cold-weather performance vary significantly between the three.