a dual constituent container includes a compartment for liquids and an elongate inwardly directed recess open to the container exterior and isolated from the compartment . the container is formed by blow molding , using a mold that incorporates a shaping feature projected longitudinally into the mold cavity . the shaping feature incorporates an arrangement of longitudinal channels having a channel width such that when a thermoplastic preform is expanded into contact with the mold cavity walls and the shaping feature , portions of the expanded preform span the channels and cooperate with the channels to provide passages that accommodate pressurized air to facilitate separation of the expanded preform from the shaping feature . the same portions of the expanded preform can partially protrude into the channels , thus to form longitudinal ribs along the recess which aid in frictionally holding a secondary constituent .