Originally a trademarked name for a container for keeping things either hot or cold for several hours. It has two silvered glass walls enclosing a vacuum, filled into a metal or plastic outer case. This design reduces the three forms of heat transfer: radiation (prevented by the silvering) and conduction and convection (prevented by the vacuum). A vacuum flask is therefore equally efficient at keeping cold liquids cold, or hot liquids hot. It was invented by James Dewar (1842–1923) about 1872 to store liquefied gases.
Preserves temperature of hot or cold drinks; SYN. thermos bottle.