Abstract: A closure assembly for a container which includes an air-impervious diaphragm which when subjected to differential pressure will expand to retain articles in place within a container. The diaphragm is retained in position by a ring member that secures the marginal portions of the diaphragm in position. the diaphragm may be secured to a container filled in a vacuum chamber so that atmospheric pressure will extend the diaphragm into the desired position or it may be subject to high pressure air to extend the diaphragm. Means for exhausting the high pressure air or for admitting atmospheric air into the interior of the container for facilitating removal of the closure assembly from the container are also described.