13 best travel mugs and thermos flasks 2023, tried and tested

Pioneers behind the first commercial flask, Thermos has since become synonymous with them, much like how Hoover is with vacuum cleaners. So, naturally, the supersize “steel king” was going to be pretty hard to beat. With a whopping 1.2l capacity, we were genuinely quite stunned by how piping hot it kept our water over 24-hours. Most of the ice in our cold drink was still solid after 24 hours too – you could fill your Thermos in the morning and it still be refreshingly cool the following day.

It’s sturdy but surprisingly lightweight for its size, and the handle, which is collapsible to save on space, helps with one-handed carrying and pouring. Everything about the steel king feels exceptionally well-made – from the thick-rimmed stainless steel cup (which doesn’t have a handle but is still nicely capacious) to the twist and pour stopper. Our one quibble would be the stainless steel cup can feel hot in your hands when the liquid inside is especially scorching. Never having to completely remove the screw cap before pouring will make for smoother al fresco pit stops. A classic for a reason, we really can’t knock it.