The biggest difference between spray foam and traditional batt (fiberglass) insulation isn’t really about R-value — it’s about air sealing. Batt insulation slows heat transfer through a material, but it doesn’t stop air from moving through gaps around it. Spray foam does both at once, which is why two homes with the “same” R-value on paper can perform very differently in real heating and cooling bills. How Batt Insulation Works Fiberglass or mineral wool batts are cut to fit between wall studs, floor joists, or roof rafters, where they work by trapping pockets of air within the material to slow