A vacuum flask or Thermos flask is a bottle that reduces heat transfer from the inside to the outside and conversely to a minimum, and therefore keeps warm drinks warm and refrigerated drinks cold. It was invented by Sir James Dewar, a scientist at Oxford University in 1892. Historically vacuum flasks have been made of glass although they are now also made in metal which makes them more durable and less prone to breakage. They comprise an outer container separated from an inner container by a vacuum; the vacuum ensures the reduction of heat transfer via convection or conduction. The interior is often silvered, reducing radiant heat transfer as well.
- Burger, R., U.S. Patent 872795, "Double walled vessel with a space for a vacuum between the walls", December 3, 1907.