This humble invention was the brainchild of Sir James Dewar, an eminent professor of chemistry at Cambridge and leading light of the Royal Institution. Dewar didn’t invent it to keep tea hot on picnics (that was a happy by product), but to help his experiments on cooling gases, like air and oxygen, to such low temperatures that they would liquefy.

A vacuum flask (also known as a Dewar Flask, Dewar Bottle or Thermos Flask) is an insulating storage vessel that greatly lengthens the time over which its contents remain hotter or cooler than the flask's surroundings. Invented by Sir James Dewar in 1892 -

over 120 years ago - the vacuum flask consists of two flasks, placed one within the other and joined at the neck. The gap between the two flasks is partially evacuated of air, creating a near-vacuum which prevents heat transfer by conduction or convection.

Vacuum flasks are used domestically to keep beverages hot or cold for extended periods of time and for many purposes in industry.