JM AP Foil-Faced Foam Sheathing

This rigid insulation from Johns Manville AP boasts an R-value of 6.5 at 1 inch, ranging up to a total R-value of 22.8. Two foil facers sit around a uniform, closed-cell, polyisocyanurate foam core that provides protection against thermal bridging and water, vapor, and air infiltration. Insulation pieces are non-corrosive and lightweight; installers can cut them with a utility knife or saw.