A ventilator of flexible material distorts to open or close

A ventilator (10) comprises an elongate housing (11) formed of plastics material containing a coaxial elongate shutter (22) also formed of plastics material, the shutter (22) being rotatable on a central longitudinal axis thereof relative to the housing (11). The housing (11) comprises two opposing walls (15, 16) which converge to an intermediate wall (14) and one of the opposing walls (15) is provided with a series of elongate slots (17). The shutter (22) is provided with a profile (23) which conforms with a profile formed by juxtaposition of the walls (14, 15, 16) and the arrangement is such that a wall (25) of the shutter (22) is retained by the walls (14, 15, 16) of the housing (11) in an open position displaced from the slots (17) or a closed position closing the slots (17) but is movable from one to the other of the positions due to flexure of the walls (14, 15, 16) of the housing (11) or the shutter (22) or the walls (14, 15, 16) and the shutter (22).