An in-wall flashing membrane for use with concrete, masonry, gypsum, or wood wall construction. Flexible 40 mil. self-adhering sheet membrane; consisting of a self-adhering rubberized asphalt, a removable silicone release film, and a high-density 8 mil. polymeric film as the top surface. Excellent tensile, elongation, and permeance characteristics. Puncture-resistant, nonremovable surface film. High-temperature resistance up to 245 deg. F. 12" x 75'.