In reply to m.hendy:
I use a Vango thermos 0.7l (I think, the label's come off).
And it's not kidding when it says "Will keep your liquid hot or cold for more than 8 hrs". I've left my thermos full overnight, and found that the liquid is still hot in the morning. Which is nice. Saves making a brew up in the freezing cold, first thing in the morning.
Unless you plan to only use your thermos for tea (or other infusion), buy a brush long enough to properly clean the inside with.
CCW