Freeze drying flasks are used in conjunction with freeze-drying instruments to facilitate sample lyophilization. A complete freeze drying flask assembly consists of a top, a bottom, and filter paper.

The flask bottom is typically cylindrical in shape and is manufactured from high-strength borosilicate glass that can withstand extreme temperature and high vacuum conditions. The top contains an opening that connects to an adapter for attachment of the flask to freeze-drying valves on the instrument. The filter paper fits into the top of the flask to prevent product loss during freeze drying.

Freeze drying flasks hold samples during low-temperature dehydration or lyophilization. The samples are frozen, a vacuum is applied, and the moisture is removed by sublimation. Freeze drying flasks are typically used in conjunction with specific freeze-drying equipment.

Freeze drying can produce better quality and more easily rehydrated samples because they are not subjected to high temperatures.

Heat-sensitive nutrients, flavors, and smells are retained, making it useful for food preservation. Freeze dried products, especially pharmaceuticals, benefit from the microscopic pores left by sublimated ice crystals, which help them rehydrate more readily. Lyophilized products are lighter without the water content and are less expensive to ship.

Other lyophilized biological products include microorganisms, vaccines, cell extracts, antihemophilic factors, interferon, streptokinase, and allergenic extracts.