A cap for a container neck includes a tubular skirt defining a central axis. The skirt includes an internal first skirt part, means for removably fixing the first skirt part to an exterior surface of the container neck, and a second skirt part. The second skirt part includes a first axial end connecting the second skirt part to the first skirt part, internally having at least one surface adapted to abut a free end of the container neck. The second skirt part also includes a second axial end opposite the first end, and an intermediate part extending between the first and second ends. Ribs project radially from the intermediate part in a direction substantially parallel to the axis. A radial dimension of the intermediate part is less than a radial distance between the exterior cylindrical surface of the first skirt part and the interior radial end of the abutment surface.