What is the difference between a thermos flask and a vacuum flask?

A thermos flask and a vacuum flask are actually quite similar in function and purpose, but there are some key differences in their usage and origin.

A thermos flask, often referred to as a thermos bottle, is a term that originated as a brand name from the Thermos Company, a manufacturer of vacuum flasks. Over time, due to the popularity of the product, the term "thermos" has become a generic term for any vacuum flask or container used to keep liquids hot or cold.

On the other hand, a vacuum flask is a more scientific and technical term. The word "flask" refers to a bottle, while "vacuum" describes the key feature of the container: the space between its two layers of glass is evacuated, creating a vacuum-like state that greatly reduces heat transfer. This vacuum insulation allows the vacuum flask to efficiently retain the temperature of its contents, whether hot or cold.

In summary, a thermos flask is a type of vacuum flask, but the term "thermos" has become a generic reference while "vacuum flask" remains the more technical and descriptive term. Both are used to keep liquids at a desired temperature for extended periods of time.