GRACE ULTRA™ butyl roofing underlayment is composed of two waterproofing materials—an aggressive 100% butyl rubber adhesive backed by a layer of high density cross laminated polyethylene film. The product is 30 mils (0.76 mm) thick making it easy to handle and apply. The unique, advanced adhesive formulation offers premium adhesion to the roof deck, high quality laps, superior seal around roofing fasteners, and unrivaled high temperature stability. The adhesive is backed by a protective plastic release liner that protects its adhesive quality. The release liner is easily removed allowing the adhesive to be bonded tightly to the roof deck.