Tamko® TW Underlayment is a flexible, self-adhering rubberized Asphalt sheet membrane with a polymer film on the surface and a removable treated release film on the adhesive side. When fasteners penetrate the TW Underlayment membrane during installation of a metal roof system, the metal roof system manufacturer's recommendations should be followed to assure watertight integrity at the fastener penetrations. TW Underlayment also provides secondary protection against water penetration after installation of the roof system. It is well suited for use as an Underlayment where prevention of water penetration is required including under metal roofs.