Specifically, in your Thermos.
The bottles that you use to keep hot liquids hot and cool liquids cool actually has two layers of metal or plastic with a "near-vacuum" in between them. The lack of air makes heat transfer very slow, significantly helping to slow temperature change of the contents.
i.e. your coffee is surrounded by "nothing", which means there's nothing to lose heat to, which is why it stays warm inside the thermos!
http://en.wikipedia.org/wiki/Vacuum_flask
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