I have the 0.5L thermos everyday food jar. It's good enough to keep soup warm until lunch time, but it isn't enough that it's piping hot come afternoon tea break.
I tend to use it more to keep things cool. Freeze sausages+bacon in it (with the lid off), put lid on and put it in pack, walk all day in summer, and by the time breakfast arrives, it's defrosted to just the right temp to cook... Sorry I digress.
J