The method involves folding a single flexible plate to form two parts (1, 2), where the parts of the plate are connected by a curved portion (3) intended to form an end of an internal volume. Radius of minimal curvature of the curved portion is ensured during assembly of the plate. The parts are assembled along two junction lines (7), where the lines laterally delimiting the internal volume of a container formed by the curved portion to form edges of the container. The plate is made of robin polyolefin film, ethylene-vinyl acetate (EVA) or EVA derivatives. An independent claim is also included for an administration assembly including a container.
