A cap for sealing a container neck includes a first skirt section, and a second skirt section. The second skirt section includes a first axial end connected to the first skirt section, a second axial end opposite the first axial end and connected to an end wall of the cap, and an intermediate section extending axially between the first and second axial ends. The cap further includes a plurality of ribs distributed around the central axis and projecting in a radial direction from at least the intermediate section towards the central axis. Each rib includes an exterior radial end connected to an interior cylindrical surface of the intermediate section, and an interior radial end radially opposite the exterior radial end. The interior radial end has at least one protrusion projecting in a direction orthogonal to the radial direction.