The stainless steel thermos comes in 2 sizes: "briefcase" 1/2 liter (the one I have) and a 1 liter size. For the full weight add about 1.05 lbs for the 1/2 liter size and 2.1 lbs for the full liter.
It really does keep things hot most of the day, and is unbreakable.
Great for winter trips. The outside metal may become very cold, so a jacket for it may be worthwhile - unsure if anything is made commercially like that.