Mule-Hide Poly ISO 1-HD Plus is an FM-approved, ½” thick high density polyisocyanurate insulation board that was specifically designed for use as a cover board in fully adhered systems. Suitable for both re-roofing and new construction applications, Poly ISO 1-HD Plus consists of a closed-cell polyisocyanurate foam core laminated to premium performance coated glass fiber felt facers. Poly ISO HD-1 Plus has an R-value of 2.5, which is significantly higher than roof cover boards made with other materials such as wood fiber or gypsum.