Abstract: A removable closure cover for a drinking vessel such as a cup or mug has an outer cover for attachment to the mouth of the vessel, with an aperture adjacent the edge through which a user may drink. An inner cover secured to the outer cover is selectively moveable into opening or closing relation with the aperture. While useable with insulated plastic drinking cups, the closure cover also may be used with traditional mug or cup forms, to enable transportation of a hot drink in sealed, insulated relation, thus extending the utility of the traditional, non-disposable mug, in an ecology promoting fashion. Manipulation of the cover provides controlled ventilation of the container and permits modulation of the cooling time for a hot drink contained therein.