thermos
A container or vessel designed to keep liquids hot or cold for long periods of time. This is accomplished by the container being composed of two flasks, one within the other, and joined at the neck. The gap between the two flasks is partially evacuated of air to produce a near vacuum which helps to impede the transfer of heat between the contents and the outside.
While these are known as a vacuum flask or vacuum bottle, these should not be confused with a Büchner flask used in laboratory vacuum filtration, which are also known as a vacuum flask.