Insulation and Air Sealing

R-value measures thermal resistance—how well a material resists heat flow. Higher R-value means better insulation. Fiberglass batts provide R-3.2 per inch—the most common and least expensive option. Cellulose (blown or dense-packed recycled paper) provides R-3.5 per inch and fills irregular cavities better than batts. Closed-cell spray foam delivers R-6.5 per inch and acts as both insulation and air barrier, but costs 3-4 times more than fiberglass. Mineral wool (rock wool) provides R-4.3 per inch with excellent fire resistance and soundproofing. Rigid foam boards (XPS, polyiso, EPS) range from R-3.8 to R-6.5 per inch and are ideal for continuous exterior insulation that eliminates thermal bridging through framing.