Dunnage Bags: How They Work and Where to Use Them

Dunnage Bags: How They Work and Where to Use Them

Dunnage Bags are inflatable restraint devices used to secure cargo within transport units such as containers, trailers, railcars, and sea vessels. Constructed from materials such as kraft paper, woven polypropylene, laminated films, or heavy-duty rubberized fabrics, these bags are inserted into voids between cargo units and inflated to create a stable, compression-based bracing system. By occupying empty spaces and exerting pressure against opposing surfaces, inflatable dunnage prevents shifting, tilting, and collapse of goods during acceleration, braking, vibration, or vessel movement.

Principles of operation are straightforward: an uninflated bag is placed into the void between cargo items, then inflated using a hand pump, electric pump, or compressed air source through an integrated valve. As the bag expands it conforms to the surfaces and develops friction and compressive resistance. This transforms loosely packed freight into an assembled load with improved load distribution and lateral stiffness. Inflatable dunnage works by three interrelated mechanisms:

• Void filling: Occupying empty spaces reduces the potential for goods to move into those voids.

• Compression and lateral pressure: Inflation presses against cargo and container walls, creating frictional resistance to movement.

• Load transfer and bracing: When properly placed, bags create continuous support surfaces that transfer forces through the load rather than allowing localized shear or impact.

Common materials and constructions include single- or multi-ply kraft (paper) dunnage, coated/inflatable woven polypropylene (woven PP) bags, and PVC or rubberized fabric bags for heavy-duty use. Kraft dunnage is often favored for single-use, lightweight palletized cargo because it is inexpensive and collapsible for disposal or recycling. Woven and laminated types are designed for reuse, higher pressures, and harsher environments—useful for heavy machinery, metal coils, or dense pallet stacks.

Key applications where inflatable dunnage is widely used:

• Intermodal containers: Prevents pallet sway and collapse in ocean and rail containers where lateral movement during lashing and sea motion can be severe.

• Truck and trailer loads: Fills gaps between palletized shipments to avoid pallet sliding and to maintain load integrity during highway braking and turning.

• Railcars: Stabilizes bulky items and reduces potential for transload damage when cargo transitions between modes.

• Specialized cargo: Paper rolls, drums, metal coils, and glass panels where rigid cushioning and uniform pressure distribution are needed.

Real-world examples illustrate typical use. A distributor shipping mixed palletized consumer goods in a 40-foot container may place 50 cm wide dunnage bags between pallet columns to stop shifting when the container transits from truck to vessel. A steel fabricator sends sheet metal coils in a domestic rail car and uses woven polypropylene bags with higher burst strength to brace coils and keep them from contacting car walls. In the food and beverage sector, breweries moving kegs in refrigerated trailers use inflatable dunnage to minimize keg-to-keg impact during sudden braking.

Benefits of using inflatable dunnage include:

• Cost-effective void control: Compared with wooden blocking or full pallet reconfiguration, bags are fast to deploy and lower in material cost.

• Flexibility: A range of sizes and materials accommodates many cargo shapes and void sizes.

• Lightweight and space-saving: Uninflated bags occupy little storage space on return trips.

• Reduced damage and claims: Proper use typically lowers incidences of cargo damage and associated insurance claims.

Limitations and considerations must be recognized. Dunnage bags are not a substitute for proper palletization, stacking, or load planning. They rely on container walls or opposing cargo units that can withstand the lateral pressure applied; fragile or deformable goods may require additional edge protection or spacer boards. Sharp edges, protruding bolts, or pallet straps can puncture bags—protective boards, corner protectors, or ethanol-resistant coatings should be used as appropriate. Environmental exposure (sunlight, extreme temperatures) can degrade some materials over time.

Standards and guidance for using inflatable dunnage are increasingly formalized in cargo packing best-practice documents and by cargo insurers. The CTU Code (Code of Practice for Packing of Cargo Transport Units) and other industry publications lay out general principles for load securing and void filling; manufacturers publish recommended inflation pressures, positioning patterns, and load limits for each bag model.

Operational best practices include pre-selecting bag type for the cargo and transport mode, measuring voids precisely, using the correct pump with pressure gauge, and sequencing inflation so the load is uniformly braced. Regular inspection of stored, reusable bags for seam integrity, valve function, and surface wear is essential.

When selected and used correctly, inflatable dunnage is an efficient, economical tool that improves cargo integrity, lowers damage risk, and simplifies loading operations across multiple transport modes.