Dunnage Bags for Container Shipping: How to Prevent Cargo Movement

Dunnage bags are an important part of cargo securing, helping maintain load stability and reduce the risk of shifting and damage. This guide covers bag selection, void filling, safe placement, inflation, common mistakes and checks before container dispatch.

Introduction

Cargo can shift inside a container when empty spaces are left between pallets, cartons, drums, crates or other loads. Braking, acceleration, turning, vibration and sea movement can then push the cargo against other loads or the container walls.

Dunnage bags, also called dunnage air bags, are used to fill suitable gaps and help keep cargo in place. When the right bag is selected and installed correctly, it can reduce movement and help protect goods during transport.

The key is not to fill every empty space blindly. The bag must suit the gap, cargo, container and transport conditions.

Why Does Cargo Move Inside Shipping Containers?

Cargo moves when it is not secured well enough to resist the forces created during transport.

Common causes include:

Gaps between cargo units
Uneven load distribution
Sudden braking and acceleration
Turning during road transport
Repeated shocks during rail transport
Rolling and other movement at sea

Cargo may also shift when there is not enough contact between load units or when the load is poorly arranged before the container is closed.

Dunnage bags are one part of a wider cargo-securing plan. Depending on the load, blocking, bracing, lashing, anti-slip material or other methods may also be needed.

How Do Dunnage Bags Prevent Cargo Movement?

Dunnage bags are inflatable bags placed in suitable gaps between cargo units or between cargo and the container wall.

After the bag is positioned, it is inflated so that it presses against the surrounding cargo. This reduces the free space in the load and limits the room available for movement.

The basic process is:

Measure the gap → Select the bag → Position it → Inflate it correctly → Check the load → Complete the securing arrangement

The bag must be strong enough for the intended use, and its working pressure and allowed gap should always follow the product specification.

How to Choose the Right Dunnage Bag?

The correct dunnage bag depends on more than the size of the empty space. Cargo weight, gap size, package shape and transport mode all matter.

The table below provides a practical starting point for common cargo situations.

Cargo Situation	Main Need	What to Consider
Palletised goods	Stop side-to-side movement	Measure gaps between pallets
Cartons and cases	Stabilise lighter loads	Check bag size and contact area
Drums and barrels	Reduce movement around curved loads	Check placement and support
Machinery and heavy cargo	Resist higher load forces	Use a bag rated for the application
Export containers	Maintain stability over long transit	Consider route and transport mode

Dunnage Bag Construction

Dunnage bags are available in different constructions. The right material and construction depend on the load, void size, handling conditions and expected transport environment.

Bubna's dunnage bag range is designed for cargo stabilisation in containers, trucks and railcars, with construction suited to different cargo-securing applications.

The important point is to check the rated performance and intended use, rather than selecting a bag only by its material name.

How to Install Dunnage Bags Safely?

Correct placement is just as important as choosing the right bag.

Measure the Void Before Selection

Measure the space between the cargo units before choosing the bag.

A bag that is too small may not provide enough support. An unsuitable large bag may also create problems if it cannot be positioned correctly.

Small gaps do not always need to be filled. The full load arrangement should be considered before deciding where a dunnage bag is needed.

Protect the Bag From Sharp Surfaces

Sharp pallet edges, metal corners and rough cargo surfaces can puncture or wear the bag.

Check the contact area before inflation and protect the bag from surfaces that could cause cuts or rubbing.

Place the Bag Correctly

The dunnage bag should sit across the intended gap and make good contact with the surrounding cargo.

It should also be positioned so that it does not create a problem when the container doors are opened.

Inflate According to the Specification

Do not guess the inflation pressure.

Under-inflation may leave the cargo loose. Over-inflation can damage the bag, cargo or surrounding structure.

Always follow the manufacturer's stated working pressure and permitted gap.

Common Dunnage Bag Mistakes

The table below shows common mistakes and the better approach for each one.

Mistake	Possible Result	Better Practice
Wrong bag size	Poor gap support	Measure the void first
Under-inflation	Cargo can still move	Follow the stated working pressure
Over-inflation	Bag or cargo damage	Stay within the specified limit
Sharp contact surface	Bag puncture	Protect the contact area
Poor placement	Load remains unstable	Position against suitable surfaces
Damaged bag	Air loss during transit	Inspect before use
Relying only on dunnage	Other movement may remain	Use the full securing method needed

A dunnage bag should support the load. It should not be used to compensate for poor loading or an unsuitable overall securing plan.

When Are Dunnage Bags Not Enough on Their Own?

Dunnage bags mainly fill suitable voids and help reduce movement. They are not a universal replacement for blocking, bracing, lashing or anti-slip measures.

The complete securing method depends on:

Cargo weight
Cargo shape
Load distribution
Void size
Friction between surfaces
Container type
Transport mode
Risk of sliding or tipping

For heavy, unusual or unstable cargo, more than one securing method may be needed.

For a broader look at protecting packaged goods during movement and storage, see Bubna's guide to preventing product damage.

Final Checks Before Container Dispatch

Before the container is closed, check that:

The cargo is stable
Required gaps have been addressed
Dunnage bags are correctly positioned
Bags are clear of sharp damaging surfaces
Inflation follows the specified working pressure
Bags will not interfere with safe door opening
Other required securing methods are in place
Damaged bags have been removed

These checks are useful for both domestic and international shipments because cargo problems are much harder to correct once the container is already in transit.

Dunnage Bags for Different Transport Modes

Dunnage bags can be used in several transport settings, but the load forces are not the same in each one.

Road Transport

Braking, acceleration and turning can create sudden movement. Void filling is useful where cargo could shift sideways or forward.

Rail Transport

Rail cargo can experience repeated shocks and vibration. Bag size, placement and load stability are important.

Ocean Freight

Sea cargo can be exposed to repeated movement during the voyage. The dunnage bag should therefore be part of a complete securing plan that suits the container and cargo.

The transport mode should always be considered when selecting the bag and the rest of the securing arrangement.

Conclusion

Dunnage bags can be a practical way to reduce cargo movement during container shipping, but correct selection and placement are essential.

Measure the gap first, choose a bag suitable for the cargo and transport conditions, protect it from sharp surfaces, follow the specified inflation pressure and use other securing methods when the load requires them.

The best cargo protection starts before the container doors are closed. A properly selected dunnage bag can help reduce shifting, impact and product damage and keep the load more stable throughout the journey.

FAQ's

Q.1. What are dunnage bags used for?

Ans. Dunnage bags are used to fill suitable gaps between cargo and help reduce movement, shifting and impact during transportation.

Q.2. How do dunnage air bags prevent cargo movement?

Ans. An inflated dunnage bag presses against the surrounding cargo and reduces the free space available for movement.

Q.3. How do I choose the right dunnage bag size?

Ans. Measure the void and consider the cargo weight, bag rating, transport mode and permitted gap before selecting the bag.

Q.4. How much should a dunnage bag be inflated?

Ans. Inflate it according to the manufacturer's stated working pressure and permitted gap. Do not guess the pressure or exceed the product limit.

Q.5. Can dunnage bags be reused?

Ans. Some dunnage bags are designed for reuse, while others are intended for one-time use. Reusable bags should only be used again when the manufacturer allows it and the bag passes inspection.

Q.6. Are dunnage bags suitable for ocean freight?

Ans. Yes. Dunnage bags can be used in containerised sea transport when the bag and the complete securing arrangement are suitable for the cargo and route.

Q.7. Do dunnage bags replace lashing systems?

Ans. Not always. Dunnage bags mainly fill suitable voids and help reduce movement. Heavy or unstable cargo may also need lashing, blocking, bracing or other securing methods.

Q.8. Can dunnage bags be used with palletised cargo?

Ans. Yes. They can be used in suitable gaps between palletised loads when the contact surfaces, bag size and overall securing arrangement are appropriate.