a container is provided in the form of a cup - like container body with a round mouth closed by a lid which becomes removably replaceable upon tearing away of a circumferentially extending tear strip which initially surrounds the mouth rim of the container body as a radially outer , integral part of the lid flange . as the lid is differential pressure - thermoformed , its radially outer region is formed into a generally inverted u - shaped structure which near the juncture of the base and radially outer leg of the inverted u , is provided , within the channel , with an inverted v - shaped notch of substantially diminished wall thickness to provide a line of weakness which preferably extends nearly fully around the circumference of the lid , but for at an angularly short tear - starting site . after the thermoforming step , and preferably in connection with trimming the lid from the surrounding scrap portion of the sheet in which it was formed , a mechanical crimper axially collapses an initially radially outwardly concave annular portion of the radially outer leg of the inverted u , intermediate the vertical extend of that leg , with an upwardly , inwardly directed barb or hook which , cooperating with the rim of the cup provides the snap lock feature for securing the lid to the cup . after the initial lidding , it is this barb which prevents removal of the lid until the tear strip is torn away .