> So I'm still not clear why a vacuum in a thermos is superior then? It's not just the vacuum, but a combination of a vacuum plus a reflective coating to deal

> So I'm still not clear why a vacuum in a thermos is superior then? It's not just the vacuum, but a combination of a vacuum plus a reflective coating to deal with the effectiveness of radiation as a heat transmission method. In this way a vacuum thermos addresses all three heat conduction methods -- conduction, convection and radiation. More here: http://wiki.answers.com/Q/How_does_a_thermos_bottle_work http://wiki.answers.com/Q/How_does_a_thermos_bottle_work This doesn't mean a vacuum thermos won't lose heat, it only means the rate of heat loss as a function of time is greatly reduced.