Abstract: A vapor barrier panel is designed specifically for application to the area between the floor joists and under the sub floor and in front of a concrete basement wall. The panel body includes a flat panel section with a flange at the top edge at right angles to the top edge and two flanges down each side. The panel body is thus applied so that the top flange engages against the underside of the sub floor and the side flanges engage against the sides and bottom respectively of the floor joists. The panel is semi rigid so they can be applied in place simply by sliding into position and abutting against a bead of sealant applied to the floor and floor joists or pre-applied to and carried on the outside surface of each flange.