A question about metal thermo flasks, or metal vacuum flasks if you prefer. I understand the principle of thermo/vacuum flasks. Just to proofed that I read up before posting this question :-) http://en.wikipedia.org/wiki/Vacuum_flask But today I had a look at on of those new-isch thermo flask contraptions totally made out of stainless metal. Its one stainless steel flask inside other with a vacuum between. But there is a stainless steel bridge connecting those two bottles at the opening. Since metal is such a good heat transfer medium – how can my drink stay boiling hot for hours?