Yes, and no crack or leak has to be involved. A sealed steel box holds a pocket of air, that air carries moisture, and once the temperature inside falls far enough the air cannot hold onto all of it anymore. The water has to land somewhere, and it lands on whatever inside the box is coldest. Source read 2026-08-19, cited below.
The moisture was already inside the box. A drop in temperature is what turns it into water.
“Cargo sweat is essentially a form of moisture damage. It occurs when the temperature inside the shipping container falls below the dew point of the air.” SSE Enterprise, Preventing Cargo Sweat and Container Rain, sse.co.th, read 2026-08-19
The dew point is the temperature at which air is fully saturated with water vapor; cool the air past it and some of that vapor has to come back out as liquid. A container loaded in a warm, humid port and later sitting through a cold night, or crossing into a different climate entirely, routinely pushes the air trapped inside below that point. Nothing has to enter the box from outside. The water was already there as vapor; the temperature drop is what turns it back into liquid.
Condensation lands in one of two places, and the trade names for the two patterns get used loosely from one source to the next. Where the water forms matters more than what a given page calls it:
When the load is cooler than the air around it, warm humid air touches the cool surface of the goods, drops past its dew point right there, and the moisture condenses exactly where it does the most damage. A load that arrived cold into a warm, humid port is the classic setup.
A container's ceiling and upper walls are exposed to outside temperature swings faster than a densely packed load is, so they can cool first and collect moisture of their own, which then drips down onto whatever is stacked underneath.
Both patterns trace back to the identical cause: warm, humid air meeting a surface colder than its dew point. Which surface cools first is what decides whether the damage shows up as a wet carton wall or a wet carton lid.
A soaked corrugated carton loses the strength it was stacked on, and it can fail under the weight sitting on top of it before anyone opens the container. Anything organic sitting in that moisture for the length of a transit run is exposed to mold. Bare metal parts, hardware, tools, machinery, start the same corrosion process water and oxygen start on any exposed steel, covered on our page about why shipping containers rust. None of that requires the container itself to have failed; a well-built, watertight box sweats on the inside from its own trapped air the same way a cold glass of water sweats on a warm counter.
The same source names two practical levers, read 2026-08-19:
Desiccants. The page names one commercial product, InterDry Power Desiccant, as rated to absorb more than 300% of its own weight in moisture — an example of what a container-grade desiccant is built to pull out of the air before the air ever reaches its dew point.
Airflow. The same page recommends good air circulation between the container surfaces and the cargo surfaces, so the load heats through quickly and evenly. A load that warms and cools at close to the same rate as the air around it never becomes the coldest surface in the box, which is the condition condensation needs.
Neither of those is something this page can price. What a desiccant kit or a particular loading pattern costs depends on the container size, the cargo and the route, and belongs to whoever is packing or forwarding the specific shipment.
Container operators, forwarders and desiccant makers describe the mechanism their own way and recommend different products for it. Treat the figures above as one source read on the date shown, and get an inspection and a real recommendation from whoever is packing or moving the specific container.
SMKlog's checkout prices United States domestic parcel labels; a sealed ocean container and the desiccant kit inside it are a different kind of shipment entirely. Loading, forwarding or leasing one goes through a person rather than the calculator on this site. Lay out the cargo, the size and both ends of the route in a freight review request and get an answer built around that specific load.
Yes, and it happens without any leak in the box. A sealed container carries warm, moist air, and when the temperature inside drops the air can no longer hold that moisture. It condenses on whatever surface is coldest, which is often the cargo itself or the steel walls and ceiling above it.
The dew point is the temperature at which air can no longer hold all its water vapor, so some of it turns to liquid. A shipping container crossing a temperature swing, day to night or one climate to another, regularly pushes the air inside below that point, and the moisture has to land somewhere.
They describe the same mechanism landing in two different places. Condensation forming directly on cargo that is cooler than the surrounding air is one pattern; condensation collecting on the container's ceiling and upper walls and later dripping onto the goods below is the other, sometimes called container rain.
Wets packaging, encourages mold on anything organic, and starts corrosion on bare metal parts. Cardboard cartons are especially exposed: soaked corrugate loses its strength and can collapse under the weight stacked on top of it before the container is even opened.
Desiccant bags or poles rated to absorb several times their own weight in moisture, and airflow. Good circulation between the container walls and the cargo lets the load warm and cool evenly instead of sitting far colder than the air around it, which is what starts the problem in the first place.
Runs SMKlog and its live rate comparisons across USPS, UPS, and FedEx. The guides here are built from the same carrier data the calculator quotes from, with prices captured on the date shown on each page. Based in Berkeley Heights, New Jersey.