Abstract: A molding system having a mechanism for securing an air barrier across the area bounded by the molding system. The molding system comprises: a bracket member and a retaining cap strip. The bracket member has a bracket width, a longitudinal axis, and a first grooved channel formed therein. The first grooved channel is oriented substantially in parallel with the longitudinal axis and has a predetermined maximum groove width. In use, the bracket member is secured to the frame work which forms the window, or other opening, with nails, screws or other fastening devices. The retaining cap strip has a cap member and an insertion member. The insertion member is dimensioned in a manner such that a terminal section of the insertion member is insertable into the first grooved channel and retained therein by contact between a portion of the terminal section and a portion of the bracket member defining the grooved channel. The cap member has a cap width greater than the predetermined maximum groove width.