Same Physics, Opposite Surfaces — and It Changes the Fix
Both come from the dew point, but they form on different surfaces and threaten different cargo. Container sweat (also called container rain) forms when the steel structure becomes the cold surface: moisture condenses on the ceiling and walls and drips down onto the load from above. Cargo sweat forms when the cargo itself is the cold surface: a cold load entering a warm, humid climate pulls condensation directly onto its own surface, like a cold drink misting in summer air.
The distinction matters because it changes what fails and what to do. Container sweat soaks cartons and packaging from the top down and is the classic enemy of hygroscopic cargo on cold-to-warm routes. Cargo sweat corrodes and stains the goods directly and is the enemy of dense, cold cargo moving into the tropics. Both are beaten the same fundamental way — keep the enclosed air below its dew point with desiccant — but loading temperature, liners and ventilation are weighted differently for each.