Thermos 184093 Light and Compact Flask, Stainless Steel, 0.5 L

You’re not likely to get the 18 hours it claims. For me, I’d say about 12 hours or so is about the limit of what would keep it hot enough for enjoyable drinking temperature and that’s assuming you pre-heat with hot water before filling it up, and that it remains full and completely unopened until that hour 12.

I will say though that performance seems to vary from one to another. With two identical models (which I believe are the same as this deal listing) one always seemed to keep noticeably hotter for longer.