Butyl Caps are a unique but proven method of sealing fasteners on metal roofs. They are round disks consisting of a tenaciously adhering butyl rubber sealant topped with a reinforcing polyester surface. Because of their ease of application, conformability, and effective water-tightness, Butyl Caps can replace the burdensome and expensive task of sealing metal roof fasteners with traditional mastics. Butyl Seam Tape is a 4-inch wide,high tensile strength, polyester-reinforced, butyl rubber sealant tape for sealing edges and seams on metal roof panels. Butyl Caps and Butyl Seam Tape should not be left exposed. They should be top-coated with AcryShield elastomeric roof coating.