It is not a thermos, it is a metal water bottle. Indeed, due to this property, it keeps cold, cold and hot, hot for a much shorter time. If it falls on hard ground from a height, it dents. Personally, I prefer it because it is metal and not plastic. Also, the spout is convenient for me because it is much easier to clean than a straw. Expensive for its quality, but the options for metal water bottles are very few and all expensive.