thermos

Everyday

1. A thermos is a special bottle or flask with two walls and a gap between them that keeps hot drinks hot and cold drinks cold for a long time. tree →
2. It is also called a vacuum flask or a flask. tree →

In the lessons

In everyday life, people take a thermos of hot chocolate or soup on picnics, school trips and walks. In science lessons, it shows insulation: the gap (a vacuum) stops heat moving in or out by conduction and convection, and the shiny inside reduces radiation. Phrases: «a thermos of tea», «thermos flask».

Examples

• Dad brought a thermos of hot cocoa to the football match. tree →
• My soup stayed hot all morning in the thermos. tree →
• A thermos keeps cold drinks cold too. tree →
• Be careful when you open the thermos — the steam is hot. tree →
• We learnt how a thermos stops heat escaping. tree →
• In the UK, people often just call it a flask. tree →

Note

Countable noun; plural «thermoses». «Thermos» was a brand name, so some write it with a capital T. «Therm» means heat (as in «thermometer»). Myth: a thermos does not make things hot; it only keeps their temperature.