Abstract: A protective cartridge mounted to a window frame has a retractable roll of blind material mounted therein. Loose steel tapes, not fastened to the blind material, are rolled with the blind material and space apart the convolutions of the rolled blind material. The blind material when extended is sandwiched between the steel tapes and magnetic strips fastened to tracks along the margins of the window frame to provide an airtight seal. The top of the blind is sealed against a rub strip portion of the cartridge and the lower portion of the extended blind material is sealed against a window sill to provide a trapped insulating air layer between the window and the blind when the blind is fully extended. Drag is bidirectionally exerted against the steel tapes to tension and position the tapes to lie flat against the blind when extended or to smoothly lie between convolutions of the rolled blind material. A combination centering guide and locking mechanism is provided at the lower end of the blind material.