Dunnage Bags

What Is a Dunnage Bag?

A dunnage bag is an inflatable load-securing product that fills the voids between cargo units, or between the cargo and the container wall, to prevent the load from shifting, tipping over, or being damaged by impact during transport. Once inflated with air, it forms an elastic cushion that fills the gap, absorbing the vibration and acceleration generated in transit to hold the cargo firmly in place.

It is widely used in sea, road, and rail freight, and is especially favored in containerized export shipments to fill the gaps between pallets, cartons, drums, rolls, or bulk cargo groups.

Material Options: Kraft or PP Woven?

There are two main material categories on the market:

• Kraft dunnage bag: Made from multiple layers of kraft paper, typically laminated with a plastic film layer to improve moisture resistance. It is single-use, low-cost, and suitable for medium-density void-filling applications.
• PP woven dunnage bag: Made from woven polypropylene fabric. It is more resistant to tearing and moisture than kraft models, making it the preferred choice for heavier loads or humid, long-haul routes.

Ply count, outer surface material, and the construction of the inner air bladder are the key variables that determine which level and application a dunnage bag is suited for.

What Does the AAR Level System Mean?

Dunnage bags are classified under the levels defined in the AAR (Association of American Railroads) Closed Car Loading Guide, published by the North American rail industry. This classification is based less on a kilogram figure the bag can withstand than on the type of void and mode of transport it will be used for:

• Over-the-road bags: Used only for full truckload (FTL) shipments, where there is no container or railcar transfer involved.
• Level 1: Designed to fill lateral voids — the gaps that form at the sides of the load — in intermodal containers.
• Level 2: Intended for longitudinal voids — the gaps that form at the front or back of the load — in intermodal containers.
• Higher levels (4–5): Reserved for heavy railcar loading and special cargo types such as paper rolls.

Some suppliers also define levels using kilogram-based lateral force ratings; however, these figures come from supplier marketing materials rather than the standard itself, and sources are inconsistent with one another. For the right choice, we recommend basing your decision on the void type and mode of transport (road, rail, or sea) of the cargo being shipped.

What Loads Is It Used For?

A dunnage bag can be used with virtually any cargo type that leaves irregular gaps once stacked. The most common applications include palletized general cargo, boxed and carton-packed goods, drums and barrels, automotive spare parts, white goods, rolled paper or textile products, and bulk bagged loads.

What these have in common is that the cargo does not sit flush against the container wall or the next cargo group, and the resulting gap allows movement during transport. The dunnage bag fills this gap to secure the cargo groups against each other and against the container body, while also preventing direct contact between loads and reducing impact damage.

How Many Dunnage Bags Do You Need?

The number of dunnage bags required depends on the container type (20ft/40ft), how the cargo is stacked, and the width of the gaps between loads. The general rule is to fill each gap completely — without creating excess pressure — using one or more bags sized to that gap's width. When a gap is very wide, using several bags side by side rather than one large bag distributes pressure on the load more evenly.

Installation and Safe Use

Dunnage bags are placed into the void after loading is complete and inflated with a compressed air gun or pump to the pressure specified by the manufacturer. For correct use:

• The bag should be centered in the gap so that no space remains at the edges.
• For sharp-edged or angular loads, using corner protection (corner board) on the surfaces the bag will contact reduces the risk of puncture.
• After inflation, the load area should be re-checked; because the cargo may settle slightly during the early stages of transport, pressure loss should be confirmed or ruled out.

Common Mistakes

• Underinflation: The bag fails to fully fill the void, allowing the load to shift during transport.
• Overinflation: On long routes with temperature fluctuations in particular, rising internal pressure can cause the bag to burst.
• Wrong level/type selection: Using an over-the-road bag in intermodal transport can mean it cannot withstand the additional loads generated during transit.
• Placement error: Leaving part of the gap unfilled or failing to center the bag greatly reduces its securing effectiveness.