The invention relates to a plastic profile which can be inserted in a rigid frame. The profile is substantially flat and longitudinal (1) and comprises at least one folding line (2) with reduced flexural rigidity, the folding line being situated between two strips (3) of the profile which can be angularly moved closer together for insertion of the profile in the rigid frame (4). The folding line (2) has a smaller thickness (s) than a thickness of the profile and is lined with elastic material, preferably rubber, with a yield point higher than the tension exerted by the rigid containing frame, when the parts are joined together.