Method of testing for a leak with the inner vessel of a double blow molded bottle

A method of testing for a leak within an inner vessel (3) of a double blow molded bottle (1), wherein said bottle (1) comprises an outer vessel (2) of a synthetic resin or resins forming the outer shell of a fixed shape and said inner vessel (3) in the form of an inner bag of a flexible synthetic resin or resins, said inner vessel being peelably laminated inside said outer vessel (2), and wherein said bottle (1) has an opening to enable the space between said outer vessel (2) and said inner vessel (3) to be exposed to the outside;

• said method comprising forming an air channel (10) between said outer vessel (2) and said inner vessel (3) by deflating and peeling said inner vessel (3) from said outer vessel (2) and by securing air flow through an opening (5) of said air channel (10), and judging the existence or non-existence of a leak through the wall of said inner vessel (3) by supplying air to said inner vessel (3) at a given micropressure and by observing, after a certain period of elapsed time, whether or not the pressure inside said inner vessel (3) reaches a predetermined level which has been set from a test conducted under the same conditions using bottles with no leak through the wall of said inner vessel (3).