The invention relates to a closure device (2) for sealing an opening of a container (1), wherein the opening (1.1) of the container (1) has an opening edge (1.2) which comprises an inner wall (1.3) and outer wall (1.4), and wherein the closure device (2) has a sealing element (4) so that the opening (1.1) of the container (1) can be tightly sealed. A closure device of this kind is characterized in that a sealing of the container (1) by the closure device (2) is independent of a contact pressure (Pk) which is applied from the closure device (2) onto the container (1), in particular onto the opening edge (1.2).