X, Y and Z

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The wording Which is a nesting, not three categories And the reverse never works Packing group is about the degree of danger So the letter is read against the material Which is the same order every property in this library arrives at The letter is only one element Element five settles liquid or solid in one character And element four settles density Read all of it, not just the letter References

X covers all three groups. Z covers one.

The wording

"(i) X--for packagings meeting Packing Group I, II and III tests; (ii) Y--for packagings meeting Packing Group II and III tests; or (iii) Z--for packagings only meeting Packing Group III tests".

Which is a nesting, not three categories

X includes everything Y covers, and Y includes everything Z covers. A more capable packaging may always carry a less demanding material.

And the reverse never works

A Y packaging cannot carry a Packing Group I material. Not because it looks weak, and not subject to judgment, but because the design type was not tested to that standard.

Packing group is about the degree of danger

I is the most dangerous, III the least, and the assignment comes from the hazardous materials table and the material's properties. That is the shipper's determination and not ours.

So the letter is read against the material

Classify first, then find the letter you need, then find a packaging marked at or above it. Three steps in that order.

Which is the same order every property in this library arrives at

Classification, then requirement, then container. Doing it backwards is the recurring failure, and here it is a shipment that may not go.

The letter is only one element

A packaging marked X may still be wrong for your material on specific gravity, on test pressure, or because it is a solids packaging and you have a liquid.

Element five settles liquid or solid in one character

A number is a liquids packaging with a tested hydrostatic pressure. The letter S is a solids or inner packagings packaging.

And element four settles density

The specific gravity the design was tested for, rounded down, which may be omitted when it does not exceed 1.2. A dense liquid needs a packaging tested for it.

Read all of it, not just the letter

The letter is the famous element and it is one of nine. A packaging that passes on the letter and fails on density is just as wrong.

References

49 CFR 178.503(a)(3), the letter identifying the performance standard under which the packaging design type has been successfully tested: "(i) X--for packagings meeting Packing Group I, II and III tests; (ii) Y--for packagings meeting Packing Group II and III tests; or (iii) Z--for packagings only meeting Packing Group III tests". law.cornell.edu

49 CFR 178.503(a)(4) and (a)(5). On specific gravity or mass: "For packagings without inner packagings intended to contain liquids, the designation shall be the specific gravity rounded down to the first decimal but may be omitted when the specific gravity does not exceed 1.2; and... For packagings intended to contain solids or inner packagings, the designation shall be the maximum gross mass in kilograms". On test pressure: "(i) For single and composite packagings intended to contain liquids, the test pressure in kilopascals rounded down to the nearest 10 kPa of the hydrostatic pressure test that the packaging design type has successfully passed; (ii) For packagings intended to contain solids or inner packagings, the letter 'S'". law.cornell.edu

Written from 49 CFR 178.503 and from the catalog as it stood on 19 October 2026. No specimen UN mark appears here, because the regulation gives its examples as images rather than as text. Nothing in this catalog is offered as UN specification packaging: we do not record whether a container carries a mark, and the mark belongs to a tested design type and is applied by its manufacturer. Packing group determinations, shipping names and documentation are the shipper's.