A grommet of resilient material having a top and bottom circumferential surfaces, wherein the body defining a central passage therethrough and defining a plurality of flanges forming an integral part of the grommet and extending inwardly from the body. The body further comprising an external holding groove extending longitudinally from the rear toward the front and extending completely around the outer periphery thereof to engage edges of the circular aperture of a beverage container. The flanges, when not engaged, forming a closed barrier across the grommet to frictionally create a hermetic seal against the passage of heat, moisture, and vapor therethrough. The flanges, when engaged, bending in a downwardly extending position against the outer surface of a straw and frictionally forming a hermetic seal between the flange and the straw.
