A closure inner shell includes an annular skirt extending axially from a base wall and having an external thread segment. The base wall may have a central passage and the skirt may have circumferentially spaced petals. A closure outer shell may include a vented plug seal extending axially through the central passage of the inner shell, and an annular outer skirt to engage the petals of the inner shell and having an internal thread segment for threaded engagement with the external thread segment of the inner shell. A container may include a container neck bead for engagement with the petals, an inner annular sealing surface for engagement with the plug seal, and an inner annular relief to cooperate with the vented plug seal to establish a vent path.