49 CFR § 178.516 - Standards for fiberboard boxes.
(a) The identification code for a fiberboard box is 4G.
(b) Construction requirements for fiberboard boxes are as follows:
(1) Strong, solid or double-faced corrugated fiberboard (single or multi-wall) must be used, appropriate to the capacity and intended use of the box. The water resistance of the outer surface must be such that the increase in mass, as determined in a test carried out over a period of 30 minutes by the Cobb method of determining water absorption, is not greater than 155 g per square meter (0.0316 pounds per square foot) - see ISO 535 (IBR, see § 171.7 of this subchapter). Fiberboard must have proper bending qualities. Fiberboard must be cut, creased without cutting through any thickness of fiberboard, and slotted so as to permit assembly without cracking, surface breaks, or undue bending. The fluting of corrugated fiberboard must be firmly glued to the facings.
(2) The ends of boxes may have a wooden frame or be entirely of wood or other suitable material. Reinforcements of wooden battens or other suitable material may be used.
(3) Manufacturing joints. (i) Manufacturing joints in the bodies of boxes must be -
(B) Lapped and glued; or
(C) Lapped and stitched with metal staples.
(ii) Lapped joints must have an appropriate overlap.
(4) Where closing is effected by gluing or taping, a water resistant adhesive must be used.
(5) Boxes must be designed so as to provide a snug fit to the contents.
(6) Maximum net mass: 400 kg (882 pounds).
(7) Authorization to manufacture, mark, and sell UN4G combination packagings with outer fiberboard boxes and with inner fiberboard components that have individual containerboard or paper wall basis weights that vary by not more than plus or minus 10% from the nominal basis weight reported in the initial design qualification test report.