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Polyiso insulation produced by Carlisle Syntec is a rigid roof insulation panel composed of closed-cell Polyiso foam bonded to two different types of facers. The InsulBase brand incorporates glass reinforced felt (GRF) facers while the SecurShield brand incorporates Coated Glass Fiber (CGF) facers. Polyiso boards can come in a variety of thicknesses and thus have a range of R-values. Rigid cellular Polyiso roof insulation board is the most widely used insulating material for above-deck commercial roof construction in North America. In commercial roofing assemblies, one or more layers of Polyiso are placed above the roof deck (typically steel, concrete, or wood) and beneath the roofing membrane. The Polyiso boards may be attached to the roof deck with various mechanical fasteners and construction adhesives or held in place with ballast stones or concrete pavers placed above the roofing membrane. The roofing membrane also may be mechanically attached through the Polyiso insulation, adhered to the top Polyiso facer or held in place with ballast. Additional common elements of this construction may include air retarders, vapor barriers, and thermal barriers placed beneath the Polyiso insulation and cover boards placed between the Polyiso insulation and the roofing membrane.