EXCEPTIONAL® Metals introduced EXCEPTIONAL® HT (high-temperature) underlayment and primer. The underlayment is a self-adhesive membrane composed of SBS-modified bitumen designed to withstand service temperatures up to 240° F (116° C). EXCEPTIONAL HT can provide a durable, walkable, temporary surface for up to 90 days until a roofing system can be installed. Enhance adhesion by applying EXCEPTIONAL HT Primer. Combined with our roof panels, metal trims and accessories, these products are part of a full portfolio of products that can be ordered together for unmatched performance and reliability.