Abstract: A secondary window includes a first glazing, a film, and a first frame. The first glazing includes a glass substrate having a thickness, between a first glazing surface opposite a second glazing surface, less than 2.0 millimeters. The film is attached to the first glazing surface. The first glazing is secured in the first frame, which at least partially surrounds the glazing. A second secondary window includes a second glazing secured in a second frame, which at least partially surrounds the second glazing. The second glazing includes (a) a first pane having a first-pane thickness less than 2.0 millimeters and (b) a second pane having a second-pane thickness that exceeds the first-pane thickness.