Container glossary
What is dunnage?
Dunnage is the loose material used to fill empty space and brace cargo inside a container so that it cannot shift — inflatable air bags, timber, boards, pads. It protects the cargo and the box, and its weight is part of the container’s declared gross mass.
How dunnage stops a load from moving
A container at sea rolls and pitches, and on road and rail it is braked hard; anything with room to move will use it. Dunnage removes the room. Air bags are placed in the gaps between rows, or between cargo and wall, and inflated until the stow is tight. Timber is cut to length and wedged or nailed as a brace across the last row. Boards and pads spread pressure and keep cargo off the steel.
It also spreads weight. A machine standing on four small feet can punch through a plywood floor that carries a forklift without harm, so timber is laid under each foot to turn a point load into an area; the limits are in the container flooring guide. Dunnage fills and props. Tying the cargo down with straps or chains is lashing, and most loads need both.
The gaps a pallet plan leaves for it
You meet dunnage on a packing instruction, a load plan or a packer’s invoice, and physically in every gap a loading pattern leaves. Twenty-five EUR pallets in a 40 ft container leave a strip 352 mm wide along one wall; that strip takes air bags, not a twenty-sixth pallet. The door end needs a brace of its own, because the last row must not be able to lean on the doors — whoever opens them is standing in front of it.
The patterns and their gaps are drawn in pallets in a 40 ft container, and the pallet calculator draws the layout for your own pallet size, so you can see the floor that is left to fill.
Untreated timber and unweighed bracing
Two mistakes recur, and both are found by someone else. The first is wood. Solid timber used as dunnage in international trade falls under ISPM 15: it must be treated and carry the mark, exactly like a wooden pallet. A brace sawn from untreated wood can get the whole consignment held at the border, and the importer pays for treatment, destruction or return. Plywood and other processed wood are exempt, which is one reason packers use them.
The second is weight. Under SOLAS the verified gross mass of a packed container includes everything in it, so when the VGM is calculated by adding up the cargo, the timber, bags and boards have to be added too. Heavy bracing left out of the sum is a misdeclared container. Count it while you build the load, not after the doors are sealed.
Frequently asked questions
What is dunnage made of?
Most often inflatable air bags, sawn timber, plywood boards, and cardboard or foam pads. The choice depends on the gap to fill and the force to resist: bags for voids between cargo, timber for bracing and for spreading heavy point loads.
Does dunnage count toward VGM?
Yes — the verified gross mass includes the cargo, packaging, pallets, dunnage and securing material, plus the tare of the container. Leaving the dunnage out understates the declared weight.
Does dunnage wood need an ISPM 15 stamp?
Yes, if it is solid wood: loose timber dunnage in international shipments must be treated and marked under ISPM 15, the same rule that applies to wooden pallets. Processed wood such as plywood is exempt.