Rigid foam is available in panels of different sizes and thicknesses. There are three basic types of foam (extruded polystyrene, expanded polystyrene and polyurethane). Polyurethane foam has the highest R-value. Some foam panels are available with a reflective foil face that can act as a radiant barrier. Although rigid foam is more suitable for new construction, it can be used in retrofit applications, but accurate cutting and fitting are required. Gaps around the edges of rigid foam are often filled with spray foam.