text: 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.