Like the CamelBak Podium Ice we tested earlier this winter (which has a much better bite valve), the Zefal Arctica is a double-wall water bottle with some foil blanket-style insulating material in the air cavity.
The inner bottle is removable, with effort, if you want to put it in the dishwasher, but it’s easier to treat it like a Thermos and clean it by hand. It’s not a Thermos, though. After two hours outside in winter, the 700ml of hot tea in ours was lukewarm.
It does slow down heat loss or build-up though, and it’s great for helping to stop water or energy drinks from actually freezing when you’re riding in sub-zero temperatures.