GenFlex Polyiso is perfect for use with virtually all membrane roofing systems. It is approved for new construction and reroofing over virtually all roof deck types. It is a highly efficient thermal insulation board with a polyisocyanurate foam core bonded to fiber-reinforced facers. GenFlex ISO products are rigid roof insulation boards composed of a closed cell polyisocyanurate foam core integrally laminated to heavy black (non-asphaltic), fiber-reinforced felt facers.