49 CFR § 178.520 - Standards for textile bags.
(a) The following are identification codes for textile bags:
(1) 5L1 for an unlined or non-coated textile bag;
(2) 5L2 for a sift-proof textile bag; and
(3) 5L3 for a water-resistant textile bag.
(b) Construction requirements for textile bags are as follows:
(1) The textiles used must be of good quality. The strength of the fabric and the construction of the bag must be appropriate to the capacity and intended use of the bag.
(2) Bags, sift-proof, 5L2: The bag must be made sift-proof, by appropriate means, such as by the use of paper bonded to the inner surface of the bag by a water-resistant adhesive such as bitumen, plastic film bonded to the inner surface of the bag, or one or more inner liners made of paper or plastic material.
(3) Bags, water-resistant, 5L3: To prevent entry of moisture, the bag must be made waterproof by appropriate means, such as by the use of separate inner liners of water-resistant paper (e.g., waxed kraft paper, tarred paper, or plastic-coated kraft paper), or plastic film bonded to the inner surface of the bag, or one or more inner liners made of plastic material or metalized film or foil.
(4) Maximum net mass: 50 kg (110 pounds).