Table of Contents
- Common types of dunnage
- Why is dunnage needed?
- Air bags: the most common type of dunnage
- How to block cargo safely
- Timber dunnage for export must follow ISPM 15
- Dunnage and VGM
- How to choose dunnage by gap, load and journey
- 7 blocking mistakes that leave cargo damaged even with dunnage
- 60-second checklist before closing the container
- Frequently asked questions
- Contact ICD Vietnam
- References
Reviewed and updated by ICD - Week 44/2026
Dunnage is the filler and bracing material used to block, support and protect cargo inside containers, trucks, rail cars or warehouses, so the load stays fixed and cannot shift in transit. When cargo does not fill the available space, the gaps let packages knock together, slide and topple when the vehicle shakes. Dunnage fills those gaps and spreads the forces, holding the cargo in place for the whole journey.
In the IMO container mass verification guidance (MSC.1/Circ.1475), dunnage is grouped with lashings and other equipment under securing material, used to block, brace and fix cargo inside a container. Dunnage only stops cargo from moving; moisture and mould also call for container desiccant hung on the walls or placed on top of the cargo.
Common types of dunnage
| Type of dunnage | Used for |
|---|---|
| Air bag (dunnage bag) | Filling the gaps between packages or pallets in a container |
| Timber dunnage (wood dunnage) | Supporting and blocking heavy cargo and creating gaps for fork tines; export timber must follow ISPM 15 |
| Foam, polystyrene, bubble wrap | Cushioning fragile cargo and filling small gaps |
| Paper corners, plastic corners, strapping | Protecting edges and holding packages tight |
Why is dunnage needed?
In transport, cargo is exposed to vibration, hard braking and ship motion, and inertia makes packages slide and strike each other. The IMO, ILO and UNECE CTU Code uses the design accelerations below to calculate cargo securing; a unit that is not blocked enough will carry a force equal to these factors multiplied by its mass.
| Mode | Forward | Backward | Sideways |
|---|---|---|---|
| Road | 0.8 g | 0.5 g | 0.5 g |
| Rail | 0.5 g (1.0 g for short impacts) | 0.5 g (1.0 g for short impacts) | 0.5 g |
| Sea, area A | 0.3 g | 0.3 g | 0.5 g |
| Sea, areas B and C | 0.3 g | 0.3 g | 0.7 g and 0.8 g |
In plain terms: when a truck brakes hard, a 10-tonne load can be pushed forward with a force equal to 8 tonnes lying horizontally. Friction between the cargo and the floor carries part of it, and the rest has to be taken by the dunnage, the lashings and the container walls. Proper dunnage reduces damage, prevents stacked pallets from toppling and makes it safe to open the container door. The detailed calculation belongs to cargo securing under the CTU Code; this article only points it out to show that dunnage is part of a force problem, not just something that fills empty space.
Air bags: the most common type of dunnage
A dunnage air bag is an inflatable bag placed in the gap between packages or between the cargo and the container wall. Once inflated, it presses and holds the cargo in place, spreads the forces and adapts itself to the shape of the load. Its advantages: light, quick to install, reusable in some types, and able to fill large gaps that timber blocking cannot. The bag level is chosen by load and mode of transport: the AAR guidance (General Information Bulletin 9) classifies bags in levels 1 to 5 with different load capacities. For selection, inflation and inspection details, see ICD Vietnam’s article on dunnage air bags (link in the VGM section below).
| Level (AAR GIB 9) | Used for |
|---|---|
| Level 1 | Horizontal gaps, mainly intermodal loads |
| Level 2 | Vertical gaps, cars with a total cargo mass up to 75,000 lbs (about 34 tonnes) |
| Level 3 | Total cargo mass up to 160,000 lbs (about 72.6 tonnes) |
| Level 4 | Total cargo mass up to 216,000 lbs (about 98 tonnes) |
| Level 5 | Vertical gaps between paper rolls lying horizontally |
How to block cargo safely
Stack the cargo tight, heavy at the bottom and light on top; fill gaps with air bags or timber; use strapping to pull packages against the wall; protect edges with paper or plastic corners; and wrap PE film to hold the pallet block together. Check again before closing the container door: any remaining gap is where the cargo will move.
Timber dunnage for export must follow ISPM 15
The IPPC standard ISPM 15 expressly covers solid wood packaging material including dunnage, because dunnage is recognised as a high-risk pathway for spreading quarantine pests. The wood must be debarked and treated by heat (HT: wood core at a minimum of 56 °C for 30 continuous minutes) or by fumigation, then marked with the IPPC mark showing the symbol, the country code, the producer code and the treatment code. Plywood and processed wood made using glue, heat and pressure, and pieces thinner than 6 mm, are exempt.
For dunnage in particular, ISPM 15 warns that cutting short pieces of wood often removes the mark: the shipper must make sure every piece of dunnage used to block or support cargo still carries a clear mark, and must not use small pieces that lack all the components of the mark. One narrow exception: dunnage supporting a consignment of sawn timber, of the same type and quality as the consignment itself, is treated as part of the consignment and not as packaging material. Timber dunnage used with an ordinary consignment must be marked.
Dunnage and VGM
The weight of dunnage counts toward the verified gross mass (VGM) of the container. Under MSC.1/Circ.1475, gross mass is the total of the container tare and every package in it, including pallets, dunnage and the packing and securing material loaded in the container. Both verification methods must include this part: weighing the whole packed container, or weighing each package together with its pallet, dunnage and securing material and adding the container tare. When a lot of heavy timber blocking is used, this part has to be added correctly. ICD Vietnam supplies dunnage air bags, pallets, PE film and blocking materials for safe container packing.
How to choose dunnage by gap, load and journey
It is not a matter of inflating an air bag whenever there is a gap, and not every air bag suits every route. Choosing the wrong blocking material can leave the cargo still moving, cause the bag to leak, or create unloading costs at the receiving end. For containerised cargo, choose dunnage by three variables: the gap to be filled, the mass and stiffness of the packages, and how rough the journey will be.
| Situation | Dunnage to use | Practical notes |
|---|---|---|
| Gap of about 10-30 cm (4-12 inches) between carton pallets | Standard level 1 air bag | Per Union Pacific loading guidance; gaps larger than 12 inches need honeycomb filler or a larger bag. Place the bag in the load-bearing zone, not against sharp edges or protruding corners of a package |
| Heavy cargo, hard contact surfaces | Timber blocking, bracing bars, combined with strapping | Export timber must follow ISPM 15 |
| Cargo that scratches or dents easily | Foam, honeycomb carton sheets, paper corners | Spread the force, avoid pressing small points onto the product surface |
| Long sea voyages | Air bags of the right level, PE film, strapping | Lateral acceleration in sea areas B and C reaches 0.7 to 0.8 g (CTU Code); choose moisture-resistant materials |
7 blocking mistakes that leave cargo damaged even with dunnage
- Blocking sideways only and forgetting lengthways: when the container brakes or the ship rocks, the load can still slide along its length.
- Placing an air bag against a sharp edge: pallet edges, steel straps or crate corners can tear the bag during the journey.
- Inflating to the wrong pressure: the CTU Code requires following the bag maker’s instructions; an under-inflated bag does not hold the cargo, and an over-inflated one can blow the valve.
- Not locking the first and last layers: when the container door is opened, the layer next to the door can fall out.
- Using materials that cannot take moisture: paper and carton weaken quickly in a damp container or with cold cargo.
- Ignoring the centre of gravity: dunnage cannot fix a heavy load stacked off to one side.
- Not taking photos before closing the door: no evidence when there is a damage dispute or an insurance claim.
60-second checklist before closing the container
| What to check | Pass when |
|---|---|
| Large gaps | Filled or locked with suitable air bags or blocking bars |
| Sharp edges | Not in direct contact with air bags, PE film or strapping |
| Cargo block | Not over the pallet load limit, not leaning, no edges sticking out too far |
| Load distribution | Heavy cargo low, even on both sides of the container |
| Container door | Opens safely, no risk of the last layer falling out |
| Records | Photos saved after blocking, before the seal is applied |
Frequently asked questions
What is dunnage?
Dunnage is the blocking material used to fix cargo, stop it shifting and protect it in containers, trucks or warehouses, filling the gaps between packages.
What types of dunnage are there?
Air bags, timber blocking, foam and bubble wrap, paper or plastic corners and strapping; each serves a different blocking purpose.
Is an air bag dunnage?
Yes. An air bag is a common type of dunnage that fills the gaps between packages or pallets in a container.
Does export timber dunnage need treatment?
Yes. Under ISPM 15, timber dunnage must be debarked, heat treated or fumigated and marked with the IPPC mark. The narrow exception is timber supporting a consignment of sawn timber of the same type as the cargo.
What should I base the choice of air bag on?
The gap, the load and the mode of transport; each bag level has a different holding capacity according to AAR guidance.
Does the weight of dunnage count toward VGM?
Yes. Under MSC.1/Circ.1475, the mass of pallets, dunnage and securing material is part of the container’s gross mass, so it must be added to the VGM.
Contact ICD Vietnam
ICD Vietnam Industrial Manufacturing Co., Ltd. - advice on pallets, plastic crates, PE film, forklifts and packaging solutions.
Hotline: 0983 797 186 / 090 345 9186
Email: sales@icdvietnam.com.vn | Zalo: Chat on Zalo
References
- IMO, MSC.1/Circ.1475 Guidelines regarding the Verified Gross Mass of a Container Carrying Cargo (2.1.6 gross mass, 2.1.10 securing material, 5.1 the two methods) - wwwcdn.imo.org
- IMO, CTU Code - imo.org: code of practice for packing and securing cargo in containers (chapter 5 on accelerations, Annex 7 on air bags)
- UNECE, IMO/ILO/UNECE Code of Practice for Packing of Cargo Transport Units - unece.org: full text of the CTU Code
- IPPC, ISPM 15 Regulation of wood packaging material in international trade (dunnage, heat treatment, IPPC mark) - ippc.int
- Union Pacific, Air Bag Placement and Usage Guidelines for Securing Intermodal Pallet Loads - up.com
- AAR, Intermodal Loading Publications, General Information Bulletin 9 (air bag levels) - aar.com
- International Safe Transit Association (ISTA) - ista.org
