Rigid foam board is a lightweight sheet insulation material manufactured from polystyrene, polyurethane, or polyisocyanurate that maintains dimensional stability and structural integrity. These boards provide consistent R-values ranging from R-3.5 to R-8 per inch thickness, with uniform thermal performance across the entire surface without settling or degradation over time.
Material Types and Applications
Expanded polystyrene (EPS) offers R-3.6 per inch at lower cost for non-demanding applications. Extruded polystyrene (XPS) delivers R-5 per inch with superior moisture resistance suitable for foundation and below-grade insulation. Polyurethane and polyisocyanurate boards reach R-7 to R-8 per inch, accommodating high R-value requirements in confined spaces like cathedral ceilings or metal frame buildings.
Installation and Building Science
Rigid boards install as complete sheets with taped seams, creating continuous insulation layers that minimize thermal bridging. They require proper vapor barrier integration depending on climate zone and application location. Common thicknesses range from 1 to 4 inches, with applications in exterior sheathing, roof decks, and foundation walls where dimensional stability prevents settling-related air gaps that compromise performance.