Vacuum flask

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A vacuum flask (also called Dewar flask, Dewar bottle, thermos or simply Dewar) is an insulating storage vessel that greatly lengthens the time over which its contents remain hotter or cooler than the flask's surroundings.


The vacuum flask consists of two flasks, placed one within the other and joined at the neck. The gap between the two flasks is partially evacuated of air, creating a near-vacuum which significantly reduces heat transfer by conduction or convection. Some vacuum flasks are shaped like a cup and are used for making cooling baths.

Cryogenic storage dewars are specially designed vacuum flasks meant to store cryogenic liquids for extended periods of time.


Vacuum flasks can be bought from lab suppliers and online. Price depends on the quality of the flask, good dewars are quite expensive. Cryogenic storage dewars are even more expensive, and are difficult to find.

Lower quality vacuum flasks can be bought from hardware stores, though they aren't very good compared to the lab version.

DIY vacuum flask

Various all-polystyrene caped cups, boxes and other containers can be used to store cryogenic materials, usually best used for storing dry ice. The thicker the styrofoam walls are, the better it insulates. Some can be found in certain stores, such as hardware stores or in school/office supplies stores.

Double wall stainless steel ice buckets can be used as open dewars, though their use is limited, and can mostly be used for cooling baths. They are generally unsuitable for storing liquid nitrogen and have limited use for dry ice.


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