A 3D flexible pouch to be filled with a biopharmaceutical product, preferably by means of at least one flexible supply line (T1, T2), and provided with at least one connection port (4, 6) for filling and/or draining, the flexible pouch being designed to unfold from a flat configuration when empty to a substantially parallelepiped configuration in a filled state, the flexible pouch having: - a first wall element consisting of a film and allowing a front face to be defined, - a second wall element consisting of a film and allowing a rear face to be defined, - a first bellows and a second bellows, each connected to two lateral edges (8, 9, 18, 19) of one and the other of the first and second wall elements (2, 3), the first bellows and the second bellows consisting of respective films (111, 112) cut in one piece and each able to fold toward the interior along a fold line (FL1, FL2) which extends between two opposite ends (14, 15) of the flexible pouch, and - said connection port (4, 6), formed exclusively in one of the first wall element and the second wall element, the first wall element and the second wall element being welded together along a so-called transverse direction to one at least of the two opposite ends (14, 15), wherein the first wall element and the second wall element have a given dimension along said transverse direction which is, at least in the flat configuration, substantially the same: - in said front and rear faces (2a, 3a), - and at one at least of the two opposite ends (14, 15), where a continuous weld (140, 150) extends over the totality of the given dimension, Knowing that in the parallelepiped configuration: - the maximum extension of each of the first and second bellows (11, 12) is at least 15 cm between the first wall element and the second wall element; and - the flexible pouch allows delimiting an interior space at least equal to 2L, said continuous weld (140, 150) also allowing, in the same end (14, 15) of the pouch, retaining, in a folded state, an edge portion (11a, 11b) of the first bellows and an edge portion (12a, 12b) of the second bellows, both in the flat configuration and in the parallelepiped configuration, characterized in that the material of the four films (102, 103, 111, 112) is identical. - a first wall element consisting of a film and allowing a front face to be defined, - a second wall element consisting of a film and allowing a rear face to be defined, - a first bellows and a second bellows, each connected to two lateral edges (8, 9, 18, 19) of one and the other of the first and second wall elements (2, 3), the first bellows and the second bellows consisting of respective films (111, 112) cut in one piece and each able to fold toward the interior along a fold line (FL1, FL2) which extends between two opposite ends (14, 15) of the flexible pouch, and - said connection port (4, 6), formed exclusively in one of the first wall element and the second wall element, the first wall element and the second wall element being welded together along a so-called transverse direction to one at least of the two opposite ends (14, 15), - in said front and rear faces (2a, 3a), - and at one at least of the two opposite ends (14, 15), where a continuous weld (140, 150) extends over the totality of the given dimension, - the maximum extension of each of the first and second bellows (11, 12) is at least 15 cm between the first wall element and the second wall element; and - the flexible pouch allows delimiting an interior space at least equal to 2L, said continuous weld (140, 150) also allowing, in the same end (14, 15) of the pouch, retaining, in a folded state, an edge portion (11a, 11b) of the first bellows and an edge portion (12a, 12b) of the second bellows, both in the flat configuration and in the parallelepiped configuration,