An insulated glazing unit comprising: - a frame comprising a base, a cross member placed above the base and two upright members for connection between the cross member and the base; - at least two at least partially transparent panes that are applied to the frame, said at least two panes and said frame defining a closed volume; - a light ray shielding device arranged within said closed volume; - support means mechanically connected to said cross member and operably associated with said light ray shielding device in supporting relationship thereto; - said light ray shielding device comprising a plurality of slats and a bottom member, said slats being connected to each other and to the bottom member, said light ray shielding device being adapted to alternate between a raised position in which the slats and the bottom member are compacted together and a deployed position in which the bottom member is placed proximate to said base; characterized in that it comprises: - first stationary guide means located at said base of said frame; - second moving guide means located on the bottom member of said light ray shielding device; wherein: - the bottom member is configured to alternate between a first configuration in which said bottom member is able to slide toward/away from the base thereby defining a slide direction, and a second configuration in which said bottom member is placed proximate to the base and is tilted to the slide direction; - the first and the second guide means are configured to contact each other when said light ray shielding device is in the deployed position and to alternate the bottom member from the first configuration to the second configuration. - a frame comprising a base, a cross member placed above the base and two upright members for connection between the cross member and the base; - at least two at least partially transparent panes that are applied to the frame, said at least two panes and said frame defining a closed volume; - a light ray shielding device arranged within said closed volume; - support means mechanically connected to said cross member and operably associated with said light ray shielding device in supporting relationship thereto; - said light ray shielding device comprising a plurality of slats and a bottom member, said slats being connected to each other and to the bottom member, said light ray shielding device being adapted to alternate between a raised position in which the slats and the bottom member are compacted together and a deployed position in which the bottom member is placed proximate to said base; - first stationary guide means located at said base of said frame; - second moving guide means located on the bottom member of said light ray shielding device; - the bottom member is configured to alternate between a first configuration in which said bottom member is able to slide toward/away from the base thereby defining a slide direction, and a second configuration in which said bottom member is placed proximate to the base and is tilted to the slide direction; - the first and the second guide means are configured to contact each other when said light ray shielding device is in the deployed position and to alternate the bottom member from the first configuration to the second configuration.