Container rain is condensation that forms on the ceiling of a cargo container and drips onto the cargo causing moisture damage.

　　During the container shipment and storage, the diurnal temperature change made the gas-rich air temperature supersaturated, which was locked in the container during the day. the cargo usual go through the hot temperature maritime climate and big difference in temperature, which could be between 0 ℃ -80 ℃ and the humidity could be up to 98%. We call it the dew condensation phenomenon. When the temperature is 30 ℃, the water content of the air is 30.4g/m3, if the temperature from 30 ℃ to 18 ℃ lower, the water vapor content will be reduced to 15.4 g/m3. Other water vapor condenses into water, which is commonly known as "container rain". It would cause a very negative impact to the goods packing image, so, we need a certain quantity of dry pole to solve this problem.