Dunnage

What it means

The federal cargo securement rules define dunnage as "all loose materials used to support and protect cargo" and a dunnage bag as "an inflatable bag intended to fill otherwise empty space between articles of cargo, or between articles of cargo and the wall of the vehicle."^[1] The same section defines a void filler as material that fills the space between cargo and the vehicle structure and is strong enough to stop the cargo from moving.^[1]

Dunnage does three jobs. It fills voids so the load cannot build up speed and hit the walls or doors. It spreads and supports weight, for example timber under a heavy crate or on top of a soft layer. It protects surfaces, keeping corners from crushing, cartons from rubbing and freight off a floor that may be wet or dirty. The IMO, ILO and UNECE informative material on container packing treats dunnage and inflatable dunnage bags that bear on fixed structures as a form of blocking, which it calls the primary method of cargo securing.^[3]

Dunnage also has weight. The same material says the mass of securing materials and dunnage counts against a container's maximum payload, and a packer planning a load should estimate it and add it to the cargo and the container tare.^[3]

Types of dunnage

Dunnage in ocean containers vs. trailers

In a domestic trailer the dunnage is part of how the load meets the securement rules for the trip. In an ocean container it has to last a longer and rougher trip with more handling, rolling at sea and changes in temperature. The CTU informative material says the total of void spaces in any horizontal direction should not exceed 15 cm, and that gaps between dense, rigid items such as steel, concrete or stone should be even smaller.^[3] Airbags and timber bracing are common ways to close those gaps.

Wood used in an import container also brings a plant health issue a domestic trailer does not have. That is covered under ISPM 15 below.

Moisture and wet dunnage

Wet or green timber can be a source of moisture inside a sealed box. The CTU informative material lists timber bracings and pallets among the sources of humidity behind condensation damage, such as mildew, rot, corrosion and cardboard that breaks down, and says it is of utmost importance to control the moisture content of the cargo and of any dunnage used.^[3] If freight arrives damp, stained or moldy, see our guide to wet cargo in a container.

ISPM 15 and wood dunnage

U.S. rules list dunnage by name as wood packaging material, along with crating, pallets, packing blocks, drums, cases and skids.^[4] CBP covers the same items, including pieces of wood used to support or brace cargo.^[6] Regulated wood packaging must be treated and carry the IPPC mark showing the country, the producer and the treatment type, such as HT or MB, and an inspector may order unmarked material re-exported.^[5] APHIS lists inflated dunnage among the alternatives that are not subject to its wood packaging regulation.^[7] For treatment, marks and what happens at the border, see our ISPM 15 guide.

Dunnage and cargo securement rules

Under 49 CFR 393.106, cargo must be firmly immobilized or secured by structures of adequate strength, "dunnage or dunnage bags, shoring bars, tiedowns or a combination of these."^[2] Dunnage is one of the named tools, not a separate rule. How many tiedowns a load needs, working load limits and commodity rules are covered in our guide to cargo securement rules.

Why it matters

Load shift and crush damage often start with gaps and poor support, not with the freight itself. Good dunnage keeps a load tight and dry, and the way a load was braced is part of the record if there is a damage claim. For international freight, wood dunnage without a valid ISPM 15 mark can cause a hold at the port even when the cargo is fine. On the receiving side, dunnage is waste that takes time and space to clear, so it is worth knowing what is coming in before the doors open.

Example

Illustrative only: a 40-foot container of boxed furniture is loaded with two rows of pallets, leaving a gap of about 20 inches near the doors. The packer fills it with an inflatable airbag between the last two stacks, puts corner protectors under the straps and lays plywood separator sheets between the tiers. The bracing at the front wall is heat-treated lumber with an ISPM 15 mark. When the box is unloaded, the crew deflates the airbag, sets the dry lumber aside for reuse and logs one damp board found near the doors.

What happens to dunnage after unloading

Once a container or trailer is devanned, the dunnage is still on the dock. A typical receiving crew handles it in a few steps:

1. Look before pulling it. Note and photograph wet wood, burst airbags or shifted bracing, since they can explain damage found later.
2. Remove it safely. Deflate or cut airbags, pull nails and blocks, and clear loose pieces from the floor so forklifts and staff are not working around debris.
3. Sort it. Keep clean, dry lumber or reusable bags if the site reuses them, and set aside anything wet, broken or contaminated.
4. Dispose of the rest. Follow the site's rules and any instructions from the shipper or importer, especially for imported wood.

For how a full devanning job works, see container unloading.

Frequently asked questions