All substances can be in liquid, solid or gaseous state. Their state of aggregation is the effect of pressure and temperature. The liquid is converted to a gaseous state by evaporation, and the solid is converted into a gaseous state by sublimation. Separating a liquid or solid from the gas phase is referred to as condensation. Since normal ambient air contains approximately 10 g of water vapor per cubic meter, condensed water vapor is present on all surfaces.

Due to the strong polarity of the water molecules, the adsorption of the surface is particularly pronounced. Natural fibers, especially paper, contain a large amount of moisture that escapes from the process during drying under vacuum. The condenser is used to separate water vapor. Even some metals (cadmium, zinc, magnesium) can evaporate in large quantities at several high temperatures of 100 °C. Therefore, avoid using these metals in equipment construction.