Goods that leave a factory in Guangdong in perfect condition can arrive in Europe rusted, mouldy or water-stained without the container ever leaking. The cause is physics inside a sealed steel box crossing multiple climate zones over thirty-plus days. This article is for companies shipping FCL and LCL from China and covers what actually causes in-transit damage, what to specify to prevent it, and the wood-packaging rule that stops shipments at the border.
Why a sealed container rains inside
A loaded container leaves a hot, humid Chinese port carrying warm, moisture-laden air — and moisture inside the cargo itself, in cardboard, wooden pallets and the goods. As the vessel moves through cooler waters, the steel roof and walls cool faster than the air inside. Moisture condenses. Two distinct forms:
- Container sweat — condensation forms on the container ceiling and walls, then drips onto cargo from above. Damage appears on top tiers and shows as water staining.
- Cargo sweat — condensation forms directly on the cold surface of the goods when warmer, damper air contacts them. Typical when a container moves from cold to warm.
Day-night cycles repeat this over weeks. The result is rust on bare metal, mould on paper, cardboard and wood, delamination of printed cartons, and softened cartons that collapse under stack load.
What actually controls it
- Desiccant, sized properly. Container desiccant bags hung on the walls absorb moisture through the voyage. Quantity depends on cargo moisture content, packaging materials and voyage length — a full 40ft on a long routing typically needs several kilograms of desiccant, not the token two bags a factory will supply if you leave it unspecified. Specify the quantity and type; do not leave it to the loader.
- VCI for metal. Vapour corrosion inhibitor film and paper release compounds that form a protective molecular layer on metal surfaces. It works in the vapour phase, so it protects recesses and internal surfaces that oil coating never reaches — and unlike oil, it does not need cleaning off before use. For steel and machinery this is the single highest-return specification.
- Moisture barrier bags for sensitive goods, ideally sealed with desiccant inside, so the microclimate is controlled independently of the container.
- Humidity indicator cards inside sample cartons. They cost almost nothing and turn "the container must have leaked" into evidence about what actually happened — which matters directly for a damage claim.
- Dry the cargo and packaging before loading. Wooden pallets and cartons stored in a humid warehouse arrive already carrying the water that will later condense. Loading during rain, or into a wet container, ruins everything downstream.
- Do not block the vents. Standard containers have vents; cargo stacked flush against them defeats what little passive ventilation exists.
Mechanical protection: stack, shift and crush
Moisture gets the attention, but crush and shift damage are more common:
- Carton strength must match the stack. Specify board strength by a measurable standard — edge crush or burst — not "strong carton". The full packaging hierarchy is in packaging development in China.
- Dunnage and void filling. Empty space is where a load shifts. Airbags, timber bracing and filler are cheap; a shifted pallet that crushes the cartons beneath it is not.
- Lashing for heavy or irregular loads. Machinery, coils and anything with a high centre of gravity must be secured to the container, not merely placed in it — for dense cargo this interacts with weight distribution, as in container loading calculations.
- Palletise where it makes sense. Pallets protect against floor moisture and speed handling, at the cost of some container volume — and that trade-off should be calculated, since carton and pallet dimensions determine how much fits.
- Stretch wrap plus corner boards for palletised stacks, wrapped to the pallet rather than just around the goods.
ISPM-15: the rule that holds shipments at the border
Any solid wood packaging material — pallets, crates, cases, dunnage, bracing — used in international trade must comply with ISPM-15: treated (heat treatment or approved fumigation) and stamped with the IPPC mark showing the country code, the treatment facility and the treatment method.
What importers get wrong:
- It applies to dunnage and bracing, not just pallets. A single untreated piece of timber used to brace a load can compromise the whole container.
- The mark must be present and legible. Treated wood without a visible IPPC stamp is treated as untreated.
- Processed wood is exempt — plywood, OSB and particle board are manufactured in ways that satisfy the requirement, which is why plastic or plywood pallets sidestep the issue entirely.
- Non-compliance is expensive and slow: fumigation at destination, re-export or destruction, plus the demurrage running the whole time — see demurrage and detention.
If your product ships regularly, plastic pallets or plywood cases remove an entire category of border risk permanently.
What to write into the order
- Desiccant type and quantity per container, with placement
- VCI film or paper for all bare or plated metal, specified by type
- Moisture barrier bags for sensitive components, sealed
- Carton board strength to a named standard, plus drop and compression testing
- Dunnage, airbags and lashing requirements for the load pattern
- Pallet type: ISPM-15 treated with a legible IPPC mark, or plastic/plywood
- Humidity indicator cards in a defined number of cartons
- A photographic loading report before the doors close — the last chance to catch a packing failure while it is still the factory's problem
This belongs in the specification and the contract, not in a WhatsApp message the week of loading — see the technical spec sheet for a Chinese factory and what a contract must contain. Verification belongs with the pre-shipment inspection, as in quality control when importing from China.
Nobody inspects packing, because packing is not the product. Then a container arrives with rust on the goods, mould on the cartons and a crushed bottom tier, and it turns out the packing was the product for thirty-five days.
Specifying packing that survives the voyage
We write the moisture, mechanical and wood-packaging requirements into the factory documentation, verify them at loading with a photographic report, and read arrival damage back into the next order's specification. Seven years and 3,500+ deliveries — real projects are in our case studies.
See custom packaging, quality inspection or logistics from China.
