In-transit damage is one of the most expensive silent leaks in international freight. Carriers reject claims when surveys show inadequate securing. Importers absorb rework, scrap, and chargebacks. And the root cause is rarely a single rough voyage — it is void space, wrong dunnage, or load plans that looked full on a spreadsheet but left tonnes of cargo free to move.
This guide explains what dunnage does, how blocking and bracing work in dry containers, common materials and when to use them, and how load planning with Palletizr reduces voids before you buy a single airbag.
Why cargo moves even when the container looks full
Ocean containers experience longitudinal surge, lateral roll, and vertical bounce — amplified when rail or road legs follow the ocean move. Anything not positively restrained shifts toward the weakest gap.
Three failure modes dominate claims files:
- Unfilled voids — cartons collapse into empty lanes and domino.
- Point loading — heavy skids on weak cartons without spreader boards.
- Top-heavy stacks — high centre of gravity without lateral lash to side rails.
A container can be 100% full by volume and still fail securing if the mass is unevenly distributed or soft packages sit under rigid steel.
Dunnage vs. lashing: different jobs
| Method | Purpose | Typical materials |
|---|---|---|
| Void fill / dunnage | Occupies empty space; prevents collapse | Airbags, honeycomb, foam, kraft, inflatable dunnage |
| Blocking | Prevents movement toward doors or walls | Timber chocks, steel brackets, prefab bracing kits |
| Bracing / lashing | Ties load to anchor points | Polyester webbing, steel wire, ISO corner posts |
| Friction mats | Increases resistance on floor | Rubberised mats under steel coils or machinery |
CTU Code (IMO/ILO/UNECE Code of Practice for Packing of Cargo Transport Units) expects the shipper to ensure cargo is packed and secured so it does not damage the CTU or other cargo and does not shift dangerously. That liability sits with the stuffing party, not the vessel operator, in most B/L regimes.
Step-by-step securing workflow
1. Build from the walls inward
Place heaviest, rigid units on the floor against the front wall (away from doors). Keep centre of gravity low and centred. Light crushable cartons belong on top, not under machinery feet.
2. Eliminate voids before lashing
Measure residual gaps after primary stacking. Gaps over 50 mm in crushable freight lanes need fill — airbags, honeycomb, or cut cardboard — before webbing goes on. Lashing across a void does not substitute for fill; it merely compresses the stack until something tears.
3. Block door-facing rows
The last row before doors is the highest shift risk during road haul. Use timber chocks, disposable bracing beams, or disposable steel prefabs rated for the expected G-force. Never rely on cardboard friction alone for steel or beverage pallets.
4. Lash to rated anchor points
Use corner castings and lash rails as designed. Cross-lash in X patterns when unit loads are tall. Avoid attaching webbing to unrated door gaskets or corrugated-only partitions.
5. Photo-document before seal
Capture four corners, door row, and lash angles. Photos win disputes when terminals argue pre-existing damage.
Material selection by cargo type
Cartons / FMCG: Inflatable airbags in lateral voids; honeycomb top-fill for partial tiers; avoid over-inflation that bursts cartons.
Palletised industrial goods: Timber chocks + polyester webbing; friction mats under oily or painted steel.
Machinery / OOG within dry box: Custom steel bracing kits; weld-on lugs only when permitted; verify COG decal on packing list.
Liquids / IBC totes: Secondary containment trays; lash each tote independently; never stack totes unless manufacturer certifies double-stack rating.
Mixed density loads: Separate heavy and light into distinct vertical zones — mixed-density walls fail inward during roll.
Common mistakes that trigger rework
- "Floor loaded = secured" — floor contact without fill still slides on polished container floors.
- Reusing water-damaged dunnage — degraded kraft and swollen airbags lose rated strength.
- Ignoring door-side dynamics — drivers brake hard on port exits; door-row shift is routine.
- Over-stuffing past door arch — bulging loads prevent proper door closure and invalidate securing plans.
- Skipping VGM after re-stuff — weight shifts when dunnage is added; re-weigh if material changes materially.
How load planning reduces dunnage spend
Every cubic metre of planned void is a metre you pay to fill with dunnage and labour. Digital load planning — including Palletizr — helps teams:
- Maximise cube so voids shrink before stuffing begins
- Flag overweight or top-heavy stacks before CY cutoff
- Export stuffing diagrams warehouse teams can execute without reinterpretation
- Compare 20ft vs 40ft configurations when dunnage costs would erase FCL savings
Better geometry upstream means less airbag spend, fewer reworks at origin, and cleaner delivery acceptance downstream.
Bottom line
Dunnage is not an afterthought — it is part of the product you ship. Match fill, block, and lash to cargo type, document the result, and treat CTU Code compliance as a sales promise to your customer, not a terminal checkbox.
If your team is still debating pallet counts and void percentages in separate spreadsheets, consolidate the plan once, stuff once, and let the container prove the math at sea.