There are basically two different ways for moisture to condense on products during transportation:

1. Cargo sweating:

When goods are transported from cold or temperate climate zones to tropical regions, moisture and water in the air will form condensation on the surface of the goods or their packaging.

2. Container rain:

When containers are transported from tropical or temperate climate zones to cold regions, moisture in the air will form water droplets on the inner walls of the container, which is what we commonly call container rain.

Fungi, mold, and mildew will not cause damage to goods when the relative humidity is below 55%.

The occurrence and impact of corrosion depend on various variable factors, including humidity and time. Due to the presence of variable factors, the effects cannot be described at a fixed humidity, but generally speaking, the lower the humidity, the better.

The type of product is also one of the factors to consider when deciding how much moisture to remove. This also determines the number of desiccant poles needed in the container to reduce and maintain humidity, so that the goods in the container will not be damaged or spoiled due to excessive humidity. This depends on: weather conditions during sea transport; length of sea voyage; cargo in the container; type of product and packaging material; container condition; sensitivity of the goods; moisture content of flooring, wood, other types of pallets or packaging materials.

If the container is filled with air at 90% relative humidity and 30℃, each cubic meter of air will contain 27 grams of water. If the temperature drops to 0℃, this cubic meter of air will only contain approximately 5 grams of water. The difference of 22 grams of water will condense out of the air, potentially damaging the goods.

Moisture or water is brought into the container along with the goods.

The humidity/moisture typically present in goods depends on the type of product and the relative humidity of the surrounding air during loading. Obviously, the relative humidity in tropical regions will be much higher than in temperate regions. Therefore, when goods are loaded into containers, moisture or water vapor is also brought in. For example, if a container is loaded with 5 tons of furniture, the furniture itself will contain approximately 8% to 25% humidity, which varies depending on the wood type and the degree of furniture drying treatment. This is equivalent to about 400-1250 liters of water. Some of this moisture will dissipate into the air inside the container, becoming a significant source of container condensation.

A 20-foot container has a volume of approximately 33 cubic meters. One cubic meter of subtropical air at 90% relative humidity and 32℃ contains 33 grams of water, totaling 1.3 liters of water. (At the same temperature, one cubic meter of air at 55% relative humidity contains 28 grams of water. Conversely, one cubic meter of European air at 100% relative humidity and 0℃ contains only 5 grams of water, or a total of only 0.2 liters of water. At 55% relative humidity, each cubic meter contains 3 grams of water.) Once the air temperature outside the container drops, 1.2 liters of water will condense on the inner walls of the container or the surface of other items inside the container. At 25℃ and 90% relative humidity, the moisture content in the air is relatively high. At approximately 22℃ and 50-60% relative humidity, the moisture content in the air is relatively low.