A GRP (Glass Reinforced Polyester) roof has a single-ply laminate applied on-site to a roofing deck and coated with a pigmented topcoat. Essentially plastic with fine fibers of glass, Glass Reinforced Polyester has been used for over 50 years in the construction of boats, ponds, pools, and other applications where waterproofing is essential. A GRP roof can easily last 20+ years with no maintenance.