system
Given the following post, respond as if you're commenting on Reddit:
human
My water bottle is a stainless steel, double walled, vacuum insulated vessel. It claims to keep liquids cold for up to 24 hours but only hot for 12 hours. Why are these not the same or at least close to one another?
gpt
If your cold stuff has any ice, it will have a hard time melting in there. The hot drinks will lose more energy due to the higher difference in temperature, and the biggest effect I've noticed:

If you pour any of the liquid into a cup to drink it, the air entering the vessel does much more to cool off a hot liquid than it does to heat up a cold liquid, due to evaporative effects.