a transparent thermoformed thermoplastic blister has a product bubble which protrudes from a flange which is connected to a backing card . the bubble has an access opening which is selectably uncovered by a pivotable door hinged to the flange and to a hinge panel by parallel hinges , with the hinge panel hinged to the flange to define an over - center hinge arrangement . the lengths of the hinge panel and door , as well as the spring constants of the hinges may be selected to form a closure which will tend to remain opened once opened , or alternatively one which will automatically spring closed when finger pressure on the door is released . the closure may alternatively be formed in a clamshell package . the physical manipulation of the door is similar to the throwing of a light switch , and hence is readily apprehended by new users .