Abstract: A method for producing a flexible pouch made of flexible thermoplastic material, including steps of: (i) preparing hot flexible thermoplastic material in a pasty state, (ii) placing a so-called “proximal” pre-molded insert onto a mounting such that the insert is arranged in a ring around the mounting, (iii) coating all or part of the insert with hot flexible thermoplastic material in the pasty state, (iv) locking the blow-mold shells around the insert, and (v) injecting a pressurized gas into the chamber so as to expand the sleeve from inside onto the inner surface of the mold or expand the sleeve from the outside by creating negative pressure inside the chamber.