Dunnage Bag Structure and Types: A Complete Guide

Reviewed and updated by ICD - Week 44/2026

A dunnage bag has three parts: a load-bearing outer shell of laminated Kraft paper or woven PP fabric, an inner bag of PA and PE laminated film that holds the air, and an inflation valve with a locking cap. By shell material there are three main types: Kraft paper bags, woven PP fabric bags and carton void-fill air bags made of PE/LLDPE film. In the ICD Vietnam catalogue, the usual paper bag is Level 1, while woven PP bags run from Level 0 to Level 5.

I am Le Van Thang, and I have worked in packaging supplies at ICD Vietnam since 2011. When a customer picks up a paper bag and a PP bag to compare, the first question is always “what is the difference, why is the price so different?” This article answers it with the layer-by-layer construction, the figures in the catalogue and the way strength levels are defined, so you can pick the right type for your cargo.

How is a container dunnage bag built?

A container dunnage bag is built on a multi-layer principle, each layer doing one job: the outer layer carries the load and resists tearing, the inner layer holds the air, and the valve lets air in and keeps it in. Separating the jobs lets each layer use the best material for its task, instead of asking one material to be both tough and airtight.

The outer shell: load-bearing and mechanical strength

The outer shell is the layer that touches the cargo and the container wall directly, so it carries the pressing force and resists abrasion and tearing. Its construction is the main factor that decides which pressure level the bag can take. There are two common shell materials, compared in the table below according to the ICD Vietnam catalogue.

One point is often misunderstood: “the more paper layers, the higher the Level”. Level is not counted by the number of layers but by whether the bag can withstand the test pressure of that level; manufacturers can reach the same level with different constructions. So when ordering, state the level you need, not just “a paper bag with so many layers”.

The inner bag: holding the air and stabilising pressure

The inner bag is the bag that holds the air, and it decides whether the bag is still taut when the container reaches the destination port weeks later. The material is usually PA (polyamide) laminated with PE (polyethylene). PA blocks gas much better than PE, so it holds pressure for a long time; PE is flexible and heat-seals well, so it forms a sealed weld around the bag easily. Laminating the two gives a film that is both airtight and tough.

If this layer leaks, the static pressing force falls gradually and the bag loses its ability to hold the load, even though the outer shell is intact. That is why I always tell customers: a bag that goes flat on the way is usually not a shell problem, but an inner bag pierced by a sharp edge through the shell, or a valve that was not closed tight.

The valve: speed and safety

The valve decides the inflation speed and how well the bag stays sealed afterwards. A quick-fill valve has a larger diameter than a traditional valve and lets air in faster: the diagram in ICD Vietnam documentation compares a standard 10 mm valve with a 30 mm quick-fill valve, with an inflation time ratio of about 1:3.

The valve seals itself when the gun is withdrawn, and then the cap is screwed on tight as a second layer of protection for the valve core throughout the trip. Fast inflation has a clear economic meaning in the packing warehouse and yard: one container can use many bags, and a little time saved on each bag makes the whole packing shift noticeably faster.

How are dunnage bags classified?

Dunnage bags are classified by shell material and purpose, which in turn determines load capacity and cost. The first two types secure the load inside a transport vehicle; the third is for cushioning inside a box.

Kraft paper dunnage bag: the economical choice for ordinary cargo

Kraft paper bags are widely used because the price is reasonable and they are good enough under ordinary road and sea transport. According to the ICD Vietnam catalogue, the usual paper bag is Level 1, inflated to a working pressure of 0.2 bar with a burst pressure of 9.1 PSI, in widths from 50 to 120 cm. The range currently has 12 sizes, from 50 x 100 to 120 x 240 cm.

Typical uses are fast-moving consumer goods, cartons and packaging stacked on pallets. The limits of a paper bag are that it tears easily on sharp edges if not padded, and it is not suited to many reuses because paper weakens after each compression and exposure to moisture.

Woven PP fabric dunnage bag: high load and reusable

A woven PP bag has a shell of cross-woven polypropylene threads, strong in tension and spreading cutting force across many threads, so sharp edges puncture it less easily than a paper bag. PP fabric is waterproof, so it is less affected by moisture inside the container during a long sea voyage. According to the ICD Vietnam catalogue, woven PP bags come in Level 0 to Level 5, in widths of 60 to 120 cm.

This is the type to choose for heavy cargo and cargo with sharp edges such as steel coils and machinery, and for rail cargo that needs a high level. According to General Information Bulletin No. 9 of the Association of American Railroads (AAR), Level 3 is for cars with a total cargo weight of up to 160,000 lbs (about 72.6 tonnes), Level 4 up to 216,000 lbs (about 98 tonnes) and Level 5 for the longitudinal gap between horizontal paper rolls. For a return flow between two warehouses, the ability to reuse the bag clearly lowers the cost per trip.

Carton void-fill air bag: cushioning inside a box

A carton void-fill air bag is a small, soft bag inflated at low pressure, used to cushion and fill the gap between the product and the box wall in e-commerce goods, cosmetics and glass bottles. The material is thin PE or LLDPE film; in the ICD Vietnam range the film is 20 to 40 micron thick.

This type has no AAR level because it is not used to secure container loads. The bag is inflated with a mini electric pump or an air-cushion machine at the packing table, not with an industrial compressed-air gun.

Which technical figures should you check when choosing a dunnage bag?

There are three figures to check: the level, the working pressure together with the burst pressure, and the maximum gap of each bag size. A well-built bag that is inflated to the wrong pressure or placed in a gap that is too wide will still not do its job.

Working pressure, burst pressure and pressing force

Working pressure is the inflation level at which the bag creates just enough static pressing force to turn the load into one unit; burst pressure is the level at which the bag starts to fail. According to the level table in the ICD Vietnam catalogue, the burst pressure is about three times the working pressure at every level; for example Level 1 is 0.2 and 0.6 bar, and Level 4 is 0.7 and 2.0 bar. These values match the AAR test pressures for each level closely.

If under-inflated, the bag is not stiff enough to push the cargo back when it is thrown against it; if over-inflated, the bag may burst when the container heats up and the air expands. The only way to inflate correctly is to use an inflation gun with a pressure gauge.

Maximum gap (Max Void) and bag size

Each bag size has a maximum gap that it can fill safely, set by the manufacturer; the CTU Code of the IMO, ILO and UNECE requires following those instructions. On the ICD Vietnam paper bag product page, the 80 x 120 cm bag has a maximum gap of 40 cm, the 100 x 180 cm bag 60 cm and the 120 x 240 cm bag 70 cm.

If the bag is placed in a gap wider than the maximum, it swells almost round, the face against the cargo shrinks, the holding force drops and the cargo slides easily. The bag height should be close to the height of the load but not above the top edge of the cargo. Many people use a rule that the bag should be 2 to 3 times wider than the gap; in my view that is only a quick estimate, and the maximum gap table of each code is the real reference.

Frequently asked questions about dunnage bag construction

What does the PA/PE inner layer do, and why use two plastics?

The inner bag is laminated from PA and PE to do two jobs at once. PA (polyamide) blocks gas well and helps the bag hold a stable pressure over a journey of many days. PE (polyethylene) is flexible and heat-seals well, so the bag can take the tension of inflation and has sealed welds. Laminating the two gives a film that is both airtight and tough.

How can I tell a Kraft paper bag from a woven PP bag by eye?

A Kraft paper bag has a yellow-brown paper shell with a slightly rough surface and high friction, and it tears easily when pulled hard or when it meets a sharp edge. A woven PP bag has a shell of plastic threads woven crosswise into a mesh, feels like plastic tarpaulin, is waterproof and is much harder to tear.

What is the AAR level of a dunnage bag based on?

According to AAR General Information Bulletin No. 9, each level is tied to a type of gap and the total weight of cargo in the car (for example Level 2 up to 75,000 lbs, Level 3 up to 160,000 lbs, Level 4 up to 216,000 lbs), and the bag must withstand the maximum inflation pressure and the burst test pressure of that level. The shell construction (paper or PP, how many layers) is how the manufacturer reaches the level, not the criterion for grading. An approved bag must be retested after three years.

Do carton void-fill air bags need a quick-fill valve and a compressed-air gun?

No. PE/LLDPE carton void-fill bags are only used to cushion and fill small gaps in a box, inflated at very low pressure with a mini electric pump or an air-cushion machine at the packing table. Compressed air from an industrial compressor is at a much higher pressure than this type of bag can take and easily bursts it.

If I need to reuse bags, should I choose woven PP or Kraft paper?

Choose woven PP bags. The woven PP shell is durable, resists abrasion and is waterproof, so the bag can be deflated and reused many times while the shell and valve are intact. Kraft paper bags weaken with each use, so they are not a good choice for reuse. Note that the CTU Code uses a lower safety factor for reusable bags (0.5 compared with 0.75 for single-use bags).

How is the quality of dunnage bags tested?

According to the ICD Vietnam catalogue, bags are drop-tested, pull-tested and vibration-tested; woven PP bags carry AAR and SGS certification and an MSDS chemical safety sheet. When export paperwork needs a certificate, ask for the one that matches the exact bag code and the exact level you plan to buy.

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References

• Construction and classification of dunnage bags: International Safe Transit Association (ISTA).
• Association of American Railroads (AAR) - General Information Bulletin No. 9, Product Performance Profile for Pneumatic Dunnage.
• IMO/ILO/UNECE CTU Code, MSC.1/Circ.1497 - Annex 7 (dunnage bags, safety factor).
• ICD Vietnam air dunnage bag catalogue: PA/PE construction, Kraft paper and woven PP shells, level table, valves, quality testing; ICD Vietnam product pages consulted October 2026.