A freeze/thaw containment system for containing a biopharmaceutical composition, comprising: - a flexible pouch of a first capacity, configured to contain the biopharmaceutical composition; - a storage unit for use in freezing, storing and thawing the biopharmaceutical composition contained in the flexible pouch; - a bag of a second capacity, configured to contain a composition representative of the biopharmaceutical composition, the second capacity being lower than the first capacity; and - a casing delimiting an inside volume for housing the bag in a filled state of the bag; wherein the storage unit comprises: - a protecting body comprising two plates (12A, 12B) for protecting the flexible pouch, the protecting body comprising a longitudinal axis and having four sides (120a, 120b, 120c, 120d), the four sides comprising two longitudinal sides (120c, 120d) extending parallel to the longitudinal axis and two other sides that include a first end side and a second end side each perpendicular to the longitudinal axis, and - an attachment device for fastening the two plates (12A, 12B) so that in an assembled state of the two plates, the protecting body comprises a peripheral margin that extends annularly in a protecting body reference plane, the peripheral margin being provided with at least one opening able to receive at least one port of the flexible pouch, wherein the system further comprises a rigid peripheral part, adjacent to or overlapping the peripheral margin, the rigid peripheral part being provided with a mounting set comprising three separate supporting members (91, 93, 94) for supporting the protecting body, wherein in the assembled state: - the protecting body extends planar in an empty state of the flexible pouch, along the protecting body reference plane; and - the two plates (12A, 12B) respectively form a lower surface (S') and an upper surface of the protecting body, at least one amongst the lower surface and the upper surface being a storage unit outer surface; and wherein the casing comprises at least two fastening elements (132, 133, 134) cooperating with fastening members (146, 147, 148; 146', 147', 148') included in one amongst the mounting set and the storage unit outer surface, in order to have the casing fastened along the storage unit, generally parallel to the protecting body. - a flexible pouch of a first capacity, configured to contain the biopharmaceutical composition; - a storage unit for use in freezing, storing and thawing the biopharmaceutical composition contained in the flexible pouch; - a bag of a second capacity, configured to contain a composition representative of the biopharmaceutical composition, the second capacity being lower than the first capacity; and - a casing delimiting an inside volume for housing the bag in a filled state of the bag; - a protecting body comprising two plates (12A, 12B) for protecting the flexible pouch, the protecting body comprising a longitudinal axis and having four sides (120a, 120b, 120c, 120d), the four sides comprising two longitudinal sides (120c, 120d) extending parallel to the longitudinal axis and two other sides that include a first end side and a second end side each perpendicular to the longitudinal axis, and - an attachment device for fastening the two plates (12A, 12B) so that in an assembled state of the two plates, the protecting body comprises a peripheral margin that extends annularly in a protecting body reference plane, the peripheral margin being provided with at least one opening able to receive at least one port of the flexible pouch, wherein the system further comprises a rigid peripheral part, adjacent to or overlapping the peripheral margin, the rigid peripheral part being provided with a mounting set comprising three separate supporting members (91, 93, 94) for supporting the protecting body, wherein in the assembled state: - the protecting body extends planar in an empty state of the flexible pouch, along the protecting body reference plane; and - the two plates (12A, 12B) respectively form a lower surface (S') and an upper surface of the protecting body, at least one amongst the lower surface and the upper surface being a storage unit outer surface; - the protecting body extends planar in an empty state of the flexible pouch, along the protecting body reference plane; and - the two plates (12A, 12B) respectively form a lower surface (S') and an upper surface of the protecting body, at least one amongst the lower surface and the upper surface being a storage unit outer surface; and wherein the casing comprises at least two fastening elements (132, 133, 134) cooperating with fastening members (146, 147, 148; 146', 147', 148') included in one amongst the mounting set and the storage unit outer surface, in order to have the casing fastened along the storage unit, generally parallel to the protecting body.