In the last decades developement of efficient vacuum pumps, refrigirators, glass and other materials made it possible that new methods broke through.These methods are based on properties of materials under low pressure and were applies in different fields of physical, chemical and biological technology.

Liofilization or freeze drying is a special kind of sublimation in vacuum. If we want to separate water from materials which are sensitive to higher temperatures, it has to be done at lower temperatures. It is possible to separate water from materials at temperatures that are lower than freezing point of water that is below 273K. In this case the evaporation of water vapour from solid state - ice is called sublimation. Since vapour pressure of ice is relatively low it is inevitable that process is carried out at lowered pressure. A freezed dried material has the same volume as the frozen material at the beginning. Because of its porosity and large surface the liofilized materials are highly soluble. Freeze drying is especially useful with biological samples where all biological and chemical processes stop because of low temperature, nevertheless biological, physiological and therapeutical properties remain unchanged. Liofilization approach is used always when the quality of samples would be damaged if standard or any other method is used for drying.

When liquides to be dried bubble or boil before or during evacuation they have to be frozen at normal pressure and only then put into the drying apparatus.