Abstract: A container closure for mounting on a container is disclosed, the container being of the type comprising a container body in fluid communication with a bored container opening for the delivery of liquid from the interior of the container. The closure comprises a bored closure body having a closure outlet at one end and a closure inlet at the other end. The closure body mounts a plurality of exterior ribs for engagement with the interior walls of the container opening. The closure is particularly advantageous as it will prevent the entry of liquid or other contaminants into the container, in addition to enabling air to flow into the container during drinking which will prevent the formation of a vacuum within the container.