Cargo condensation could simply be caused by the humid air left in the container when the doors were closed. Many types of cargoes (eg. green coffee) and packing materials can also contain moisture, especially after being stored in wet or humid environments.

Pallets, dunnage wood, wooden supports, filling materials and others can also absorb and retain moisture, especially when they are made from green wood. When the container is closed and exposed to the sun, the moisture from all these sources rises to the upper layers of air, which are relatively warm. And when this air becomes saturated, the moisture condenses on relatively cool surfaces, particularly items near the floor of the container.