【英语时差8,16】了解暖水瓶的工作原理-下（在线收听）

What’s A Good Insulator? How about air? Air is, in fact, a pretty good insulator, which is why styrofoam keeps things hot. It’s full of air. But even better than that would be a vacuum. Because there’s nothing in it to heat up, heat can’t conduct through it. A vacuum is the best insulator of all, and that’s the principle behind a thermos. A thermos is a flask with a double-walled container inside it. Air is removed from the space in-between the walls. Now heat can’t escape from the soup; it’s surrounded by a vacuum. And to further help hold in heat the inside walls are silvered to reflect heat rays which try to escape.