Abstract: The system includes a plurality of movable heat insulating shutter sections forming a barrier to produce a "dead air gap" adjacent the interior of a window and increasing the heat insulation capacity of the windows. The sections are suspended by wheels, rollers or gliding fittings from guide tracks situated above the shutters and are movable therealong between opened and closed positions. The sections are provided with vertical and horizontal friction or pressure seals which, when the sections are in the closed position, seal the sections together and to the window embracement. The tracks and the suspending fittings are formed such that the sections can be pendulum-like pivoted away from the window in order to disengage the pressure of the seals and thus facilitate movement of the sections between the open and closed positions without friction at these seals.