a method for fabricating a lid for attachment to a vessel having an open top surrounded by a peripheral edge portion , includes injection molding from a molten plastic material a first shot structure defining a web portion , a peripheral portion surrounding the web portion ; in a second shot procedure , over - molding an elastomeric material different from said plastic material onto the first short structure to form a seal structure portion integrated with the lid portion to form a unitary lid - seal structure , wherein the seal structure portion is permanently adhered to the peripheral portion of the first shot structure , and wherein the seal structure portion is configured to provide an air - tight seal between the lid and a sealing surface portion of the peripheral edge of the vessel when the lid is attached to the vessel .