If you ship hazardous materials, the string of letters and numbers stamped on your container is one of the most important pieces of information in your entire packaging program. It tells you exactly what that container has been tested and authorized to carry. Knowing how to read a UN certification means you can verify, in about thirty seconds, whether the container in front of you is legally authorized for your product. Not knowing how to read it means you are trusting that someone else got it right. 

This field guide breaks down every element of a UN certification marking in plain language. By the end, you'll be able to look at any UN-marked container, decode what it's authorized to carry, and confirm whether it matches your specific product. If you want broader context on hazardous materials packaging compliance before diving into the marking itself, start with our DOT Packaging Compliance 101 guide.

What Is a UN Certification?

A UN certification is a standardized marking applied to packaging that has been independently tested and authorized to transport hazardous materials. The "UN" refers to the United Nations, which established the global framework for classifying and testing hazardous materials packaging. In the United States, these standards are adopted and enforced by the Department of Transportation under Title 49 of the Code of Federal Regulations.

The certification is not a general quality stamp. It is a specific authorization that tells you the container has passed a defined battery of performance tests, including drop tests, stacking tests, leakproofness tests, and hydraulic pressure tests depending on the container type, for a specific category of contents. A container with a UN marking has been proven capable of safely containing the type and quantity of hazardous material the marking describes.

Knowing how to read a UN certification matters because the marking is the only reliable way to confirm that a container is authorized for your product. A container can look identical to a certified one and not carry the certification. The marking is the proof, and reading it correctly is the buyer's responsibility as the shipper.

A Sample UN Marking, Decoded

Let's start with a complete example and then break down every element. A typical UN marking on a plastic pail or drum might look like this: 

UN 1H2/Y1.8/100/24/USA/M5267

Each segment of that string carries specific information. Here is what every element means:

The sections below explain each of these segments in more detail.

Element 1: The UN Symbol

Every certified container begins its marking with the letters UN, sometimes shown inside a circle as a stylized symbol. This confirms that the packaging has been manufactured and tested to United Nations performance standards.

If a container does not carry the UN symbol at the start of its marking, it is not certified for hazardous materials transport, regardless of how sturdy or well-made it appears. This is the first thing to check and the most fundamental: no UN symbol means no certification.

Element 2: The Packaging Identification Code

The packaging identification code is the heart of the UN marking. It tells you what kind of container you're looking at, what it's made from, and how it's configured. In our example, that code is 1H2.

The code is read in three parts:

The first character is a number indicating the container type:

The second character is a letter indicating the material:

The third character is a number indicating the configuration:

So in our example, 1H2 decodes to: a drum (1), made of plastic (H), with an open head (2). A steel jerrican with a closed top would be coded 3A1. A plastic jerrican with an open top would be 3H2.

This is one of the most important verification steps. If the packaging identification code describes a different container than the one you actually have in hand, the certification does not apply to your container. A marking for a steel drum does not authorize a plastic pail, even if the rest of the marking looks correct.

Element 3: The Performance Level (Packing Group)

The next segment is a single letter, either X, Y, or Z, that tells you which packing groups the container is authorized to carry. This is one of the most consequential elements of the entire marking, and one of the most commonly misread.

The logic works in one direction only. A container rated for a higher hazard level can carry materials of that level and anything below it, but never the reverse. An X-rated container can carry Packing Group I, II, or III materials. A Y-rated container can carry Packing Group II and III but not Packing Group I. A Z-rated container can carry only Packing Group III.

This is where the most expensive mistakes happen. If your product is a Packing Group I material and your container is marked Y, the container is not compliant, no matter how well it's built. Before you accept a container for a regulated product, confirm that the performance level on the marking covers your product's packing group. If you're unsure of your product's packing group, it's listed on your Safety Data Sheet and in the DOT Hazardous Materials Table.

Element 4: Specific Gravity or Maximum Gross Mass

The next segment tells you the maximum density or weight the container is authorized to hold, and how to read it depends on whether your container is intended for liquids or solids.

For liquids: The number represents the maximum specific gravity (relative density) of the contents the container is certified to carry. In our example, 1.8 means the container is authorized for liquids with a specific gravity up to 1.8. Water has a specific gravity of 1.0, so this container can safely carry liquids up to 1.8 times the density of water. If your product is denser than the rated specific gravity, the container is not authorized for it.

For solids: The number represents the maximum gross mass in kilograms, meaning the total weight of the container plus its contents, that the container is certified to carry.

A note worth flagging: specific gravity is sometimes omitted from markings for solids, where maximum gross mass is the relevant figure. The structure of this part of the marking tells experienced readers whether they're looking at a liquids container or a solids container.

Element 5: Test Pressure (Liquids Only)

For containers intended to hold liquids, the next segment indicates the hydraulic test pressure in kilopascals (kPa) that the container was tested to withstand. In our example, 100 means the container was tested to 100 kPa.

This figure matters for liquids that may build vapor pressure during transport or storage, particularly under temperature variation. The test pressure needs to be appropriate for the vapor pressure characteristics of your specific product under the conditions it will experience. For solids, this segment is typically replaced with the letter S, indicating the container is certified for solids or inner packagings.

Element 6: Year of Manufacture

The next segment is a two-digit number indicating the year the container was manufactured. In our example, 24 indicates the container was made in 2024.

The year of manufacture matters more than buyers sometimes realize. UN-certified containers have functional lifespans, and certain materials degrade over time. Plastic containers in particular can become brittle with age and UV exposure, which is why DOT regulations place limits on how long certain plastic packagings may be used to transport hazardous materials after their date of manufacture. Always check the manufacture year, especially on containers that may have been sitting in inventory.

Element 7: Country of Authorization

The next segment indicates the country whose competent authority authorized the certification. In our example, USA indicates the certification was authorized in the United States.

This element confirms that the certification was issued under a recognized regulatory framework. For materials shipped within or into the United States, the certification should reflect authorization recognized by U.S. DOT.

Element 8: Manufacturer Code

The final segment is an alphanumeric code that identifies the manufacturer and the certification. In our example, M5267 is the code assigned to the manufacturer by the certifying authority.

This code provides traceability. If a question ever arises about a container's certification, the manufacturer code allows the container to be traced back to its source and its certification records. It's the packaging equivalent of a serial number for compliance purposes.

How to Verify a UN Marking Matches Your Product

Knowing how to read a UN certification is only useful if you apply it to verify a real match. Here is the practical verification sequence to run on any container before you commit to it for a regulated product:

1. Confirm the UN symbol is present. No symbol means no certification. Stop here if it's missing.
2. Check the packaging identification code. Confirm the container type, material, and configuration match the container you actually have.
3. Verify the performance level. Confirm the X, Y, or Z rating covers your product's packing group.
4. Check the density or gross mass rating. Confirm your product's specific gravity or filled weight falls within the rated limit.
5. Review the test pressure. For liquids, confirm the test pressure is appropriate for your product's vapor pressure characteristics.
6. Check the year of manufacture. Confirm the container is within its allowable service life for your application.

If all six checks pass, the container is authorized for your product. If any one of them fails, it is not, regardless of how the others look.

Common Mistakes Buyers Make Reading UN Markings

Even buyers who know how to read a UN certification fall into a few recurring traps. Here are the ones worth guarding against:

Assuming a higher-quality container is automatically compliant. Compliance is about the marking matching the material, not about how rugged the container is. A premium container with the wrong performance level is still non-compliant.

Matching the hazard class but missing the packing group. A container can be the right type for your hazard class and still carry the wrong X/Y/Z rating for your packing group. Both have to match.

Overlooking the specific gravity rating. Buyers frequently verify the container type and performance level but forget to confirm their product's density falls within the rated specific gravity. A dense product in a container rated for a lower specific gravity is not authorized.

Ignoring the manufacture date on inventory containers. A container that was compliant when purchased may be past its allowable service life if it has been sitting in inventory for years. Always check the date.

Trusting the marking without confirming the actual container matches it. Markings can be applied in error. The marking should describe the container you actually have. If the marking says steel drum and you're holding a plastic pail, something is wrong.

Where ILLING Fits In

Reading a UN marking correctly is a skill any industrial buyer can learn, and this guide gives you the framework to do it. But verifying that every container in your packaging program carries the right certification for the right product, across multiple SKUs and changing regulatory requirements, is exactly the kind of detail where an experienced packaging partner earns their place.

ILLING has spent 100 years sourcing certified containers for industrial manufacturers across every major hazard class. When you source a container for a regulated product through ILLING, our team verifies that the certification matches your product's classification before the container goes into production. We've done this across hundreds of products and dozens of chemistries, and we know where the common mistakes hide.

If you're working through a container specification for a hazardous material and want a second set of eyes on the certification, or if you want a packaging partner who treats compliance verification as part of the job rather than the customer's problem, we'd like to hear about it.

For more on the regulatory framework behind UN certifications, see our DOT Packaging Compliance 101 guide. For guidance on matching your product chemistry to the right container material, see our guide to Chemical Compatibility Testing. And for a full overview of the pail formats most commonly used for hazardous materials, see our Industrial Pail Buying Guide. For the complete picture of rigid packaging options, start with our Complete Guide to Rigid Packaging.