G.A.P. WaterGuard™ AMT Architectural Metal & Tile Synthetic Roofing Underlayment is a polypropylene, two-side coated woven fabric containing a patented slip resistant surface. This product is used as a secondary roofing protection; mechanically attached to the roof sheathing under the primary roofing material. Its premium performance allows for use under all standard types of roofing cladding.