In 1892 Scottish scientist James Dewar needed to measure the specific heat of palladium at cryogenic temperatures, so he sealed one brass chamber inside another and pumped out the air between them. The vacuum stopped conduction and convection, and silvered walls later reflected radiant heat back inward. Dewar refused to patent the design, believing scientific tools should stay open. In 1904 German glassblowers Reinhold Burger and Albert Aschenbrenner added a protective metal case, patented the consumer version, and named it Thermos.

Dewar sued and lost because he had never filed a patent, and Gustav Robert Paulin licensed the Thermos and mass produced it in places including Norwich, Connecticut. The flask’s weak points are the neck and the stopper, and big versions need spacers that leak heat. Large Dewars hold liquid nitrogen at 77 Kelvin with slow boil off and no electricity, a nested double design holds liquid helium for MRI magnets, and NASA used vacuum flask technology in Saturn propellant tanks during Apollo.

• The Arktek vaccine carrier keeps doses under 10 degrees Celsius for weeks using eight one liter blocks of ice.
• Oil and gas crews shield wireline logging electronics inside Dewars in wells that reach 350 degrees Fahrenheit.
• Glass flasks can implode from thermal shock, while sealed cryogenic tanks risk bursting because one liter of liquid nitrogen becomes nearly 700 liters of gas.
• Industrial Dewars use pressure relief valves and corrugated expansion joints to survive.
• In 1963 a US court declared thermos a generic term, stripping the company of exclusive rights to the name.