Sill pans, arched windows and other curved penetrations complicate installs. FortiFlex® Butyl is a flexible, self-adhering waterproof flashing that is highly conformable, making it ideal for use in these applications. FortiFlex Butyl is constructed from a technically advanced hybrid butyl compound and a high-performance creped film that features exceptional stretch and durability. FortiFlex Butyl can be stretched around tight arcs, including arched windows, irregular penetrations and sill pans. It adheres tenaciously to most common construction materials, including plywood, OSB, aluminum, rigid vinyl, gypsum board, primed steel, concrete and concrete block. The unique butyl formulation maintains high tack even at installation temperatures as low as 10°F. FortiFlex Butyl self-seals to prevent moisture intrusion.