It is a vessel
for storing hot or cold liquids so that they maintain
their temperature independently of the surroundings.
The walls of the vessel consist of two thin layers
of glass separated by a vacuum to reduce conduction
and convection; inner surface of a glass vessel is
silvered to reduce radiation; and the vessel is stoppered
to prevent evaporation.
It was devised around 1872 by Sir James Dewar and is also
known by its first tradename Thermo flask.