For the type of laboratory glassware, see Büchner flask.

A vacuum flask, today most familiar in the form of the common thermos (the latter is trademarked), is a resealable canister with excellent thermal insulation properties ("keeps hot things hot, cold things cold").

Instead of only relying on a traditional thermal insulator to insulate the inside from the outside, the sealed container in fact contains a near vacuum. A vacuum does not conduct heat at all by conduction or convection, and radiation, the other form of heat transfer, is kept to a minimum by coating the internal surfaces meeting the vacuum with silver or other reflective metal.

In theory, a vacuum flask could therefore approach arbitrarily close to perfectly insulating its contents, for example keeping a cup of coffee hot for a decade. In practice, however, the inside wall of the container must meet the outside wall, usually at the mouth of the container, at which point slight heat conduction does occur between the inside and outside walls (the vacuum being in between).

The vacuum flask was invented by the Scot Sir James Dewar, while working as a scientist at Oxford University in 1892. Historically vacuum flasks have been made of glass although they are now also made in metal which makes them more durable and less prone to breakage.

The first vacuum flasks for commercial use were made in 1904 when a German company, Thermos GmbH, was formed. "Thermos", their tradename for their flasks, remains a registered trademark in some countries but was declared a genericized trademark in the US in 1963 as it is colloquially synonymous with vacuum flasks in general.

Patent

• Burger, R., , "Double walled vessel with a space for a vacuum between the walls", December 3, 1907.

See also

• Dewar flask
• Vacuum flask cooking

External links

• Thermos LLC website

Containers | Scottish inventions

Thermoskanne | termoso | Thermosfles | termoso | 魔法瓶 | Termos