What could happen to your cargo on this route?
Choose the port of loading, the port of arrival, the month, the container type and how the load is built. Using the climate normals of the last six years we calculate the risk scenarios for the voyage, ranked from highest to lowest, and conclude whether the shipment needs container desiccants and whether wooden bracing should be replaced by a method that adds no water.
Wood and cardboard hold water: a damp pallet can release several litres inside the container.
Reference scenarios calculated with 2019-2024 daily climate normals (ERA5 reanalysis, via Open-Meteo) for the ports of loading and arrival, and with typical direct-service transit times. This is not a forecast of your voyage or a quantity calculation: actual condensation also depends on the moisture of your goods and pallets, where the carrier stows the container and the weather on that particular voyage. Always confirm your shipment with a SECAL specialist.
Why a container condenses on the inside
A closed container is an unventilated space that travels for weeks through changing climates. The air sealed in at stowage carries a fixed amount of water: the amount that matches the temperature and humidity of the port of loading. When the steel cools below that air’s dew point, the vapour condenses on the roof and walls and falls on the cargo. In the trade this is called container rain, and it is the most common cause of mould, rust and collapsed boxes when the doors are opened at destination.
The water does not come only from the air
The air in a 40 ft container rarely holds more than two litres. The rest comes from the goods, the cardboard and, above all, the wood: an unseasoned pallet can hold several litres of water and release them during the voyage. That is why the same shipment, on the same route in the same month, carries a different risk depending on how it is built: damp wooden pallets braced with boards are not the same as treated, dry pallets with polyester strapping.
Cargo sweat: the risk in reverse
When cargo leaves cold and arrives at a warm, humid port — typical of shipments to Asia or the Caribbean in summer — condensation does not form on the roof but on the product itself, when the doors are opened and warm air rushes in. This is called cargo sweat, and it means keeping the container closed until it reaches the cold store and not removing the desiccant too early.
Securing: holding the load without adding water
Wooden bracing is cheap but works against you twice: it gives way as the vessel rolls and it adds moisture to the container. Lashing with polyester strapping in an X pattern, with air bags to fill the voids between stacks, holds better, can be re-tensioned when the load settles and adds not a gram of water.
What to do with this result
This tool tells you whether your shipment needs protection, not how much. Once the scheme is defined, the quantities come from the SECAL calculators: units of container desiccants per container, silica gel sachets per pack, air bags, strapping and ethylene sachets. For high-value cargo or difficult routes, validate the scheme with a SECAL specialist before shipping.