text: how a thermos flask keep cold things cold?   initially called a dewar flask, it was created by placing one bottle inside another bottle and then fusing the two mouth together. the air trapped in between the two bottles is removed, creating a vacuum. you think air is a bad heat transferer, a vacuum is even worse. that solves heat convection. to beat heat radiation, the sides of the inner bottle are coated in a reflective surface (it looks like aluminum/glass to me). last, heat conduction is stopped by using cork or rubber (also a bad conductor) for the cap.