Abstract: A system for double glazing existing panes in windows or the like in which a pane of translucent or lightaltering material is cut to the shape of the exposed surface of an existing windowpane within its sash. The additional pane is secured to the existing pane through the use of magnetically intermateable spacer strips which are secured to the added and existing panes around their outer periphery by means of an adhesive. The intermateable spacer strips are of a thickness which allows for separation of the two panes by a sufficient distance to create an air space therebetween to enhance the insulating properties of the structure. A thin flexible strip of decorative material is secured to the surface of the attachable pane opposite the existing pane along its periphery so as to overlap the adhesive on the opposite face of the attached pane while extending outward to overlap the inside edges of the sash and thereby additionally seal and insulate the area around the outer periphery of the attached pane.