VulcaSeal G40 Fiberglass (Modified) is world-class fiberglass based modified asphalt underlayment that provides the best in protection for your home and family under concrete tile, clay tile, or metal roofing. The coating material is impregnated into the Fiberglass sheeting providing it the highest standards in roofing for strength, durability, and longevity. Specially designed, patented, and manufactured by Fontana Paper Mills, Inc., VulcaSeal G40 is the most reliable and optimal way to make your roof last and your home dry.