“The heavier, the better at keeping warm” is not accurate: the weight mainly comes from the thickness of stainless steel, and the vacuum degree is the key.
Thermos cups cannot be used to hold carbonated beverages, as strong acids can increase the internal pressure or corrode the inner lining, posing safety risks.
Once the vacuum layer is damaged, it becomes essentially ineffective, and the insulation performance plummets after being bumped or dropped, usually making it impossible to repair.
The principle behind keeping a thermos bottle cold is the same as that for keeping it hot, only the direction of heat flow is reversed. It is equally effective for holding icy drinks.
