The device (1) has an omega shaped open section (3) deformed so as to be encased in or over a rigid open section (2) to fix a flexible material e.g. plastic film (6), by pinching, where the film is inserted between the sections. Parts of the section (3) are supported against the section (2) for fixing the film trapped between the parts of the section (3). The parts are covered by a protection layer (5) made of a material having hardness lower than 60 shore A and reduced relative to that of a base material of the section (3) on which the layer is applied. An independent claim is also included for a multi-bay greenhouse comprising a covering.
