a shield for facilitating ventilation of the interior of a motor vehicle , comprising a sheet of transparent semi - rigid plastic material with a flange along its upper edge containing sharp rib or barb - like protrusions near the top for fastening the upper edge of the sheet into a window trough , and a curved skirt with a flange extending outwardly from its lower edge . this keeps out rain and snow while allowing air to pass in and out of the vehicle by means of convection currents . the shield is preferably made of flexible material adapted to be cut with scissors to fit any sized window in the vehicle . in one embodiment , the flange along the upper edge is u - shaped , and flat along the top . a plurality of small metal t - shaped locks are permanently held in the flat top to lock the device into a window trough upon rotation of the locks . this embodiment also includes a row of louvered openings spaced - apart along its length to allow air to pass in and out of the vehicle . in another embodiment , the top edge has a slight inward bend with sharp ribs and is held in place in the window trough by a sponge - rubber cord . the louvers are also eliminated in this embodiment , which instead accommodates an inwardly - directed half - round sponge - rubber cord near its flanged lower end , which acts as a seal and anti - vibrator against the outer face of the window , when raised .