Abstract: A composite weather strip is disclosed having a semi-rigid elongated body and a relatively flexible extension formed in integral coplanar relation on a side edge of the body. The extension is laterally tapered to a feathered edge and has longitudinal ribs projecting from one surface of the extension. A foam tape attaches the body to one of two relatively movable surfaces, such as a frame surface and an adjoining surface of a window or door, adjacent a joint between the two surfaces. Whenever the window or door is closed, the flexible extension is engaged with the other of the two surfaces and, upon such engagement, is deflected to provide a positive seal against the passage of air through the joint in a sealing construction of exceptionally high integrity.