The desiccant method
The desiccant method is used to protect goods from damage through moisture. This means that desiccants are added to the goods within a protective barrier or an enclosed space. When correctly dimensioned the desiccant takes up humidity from the air and reduces the relative humidity to a generally safe value of approximately 40% at 20°C.
Migration of humidity
Air holds a lot more water at high temperatures than when it is cold. The maximum 100% relative humidity is an impressive 30.4 g/m³ at 30°C, but only 6.8 g/m³ at 5°C. Because humidity cannot escape through the outer barrier when temperatures drop, it sets down on the good and the packing materials. If the surrounding air heats up faster than the goods condensation will actually form on the surface of the goods.
Conversely humidity migrates out of the merchandise and/or the packaging materials into the air when temperatures rise. As an example an originally low relative humidity of 30% within the barrier can rise to 80% by using a moist wooden pallet. Transport through different climate zones is not the only reason for major temperature fluctuations. Even when the difference between strong sunshine during the day and dropping temperatures at night can cause a difference of more than 40°C within the container.
Migration of moisture from the air into or onto merchandise, e. g. in a cargo container during a sea journey
The four kinds of moisture
For correct dimensioning, all "four kinds of moisture" have to be taken into account. In this closed system, the moisture values can either be precisely calculated according to formulas or estimated from experience. More details can be found in the dimensioning section.