Here's a little trick I learned when I was working on the super secret spy monitoring facility that is 300 yards directly below the North Pole:
Preheat your thermos before you pour your coffee/tea/etc in it by pouring boiling water into the thermos and letting it sit there for a while. Then, pour it out and pour in the hot liquid of your choice. It will keep hotter for longer.
When you use this method, all I ask is that you think of me when you're enjoying your hot beveridge. Thanks, and have great day. Olyclimber.