How Long Does a Vacuum Flask Keep Water Cold?
A quality flask keeps water cold for hours — often all day with ice. Here's what affects it.
A good vacuum flask can keep water cold for many hours — often a full day, and longer if you add ice. The exact number depends on the flask's insulation quality, how full it is, and how often you open it, but quality double-wall vacuum bottles are designed to hold cold drinks cold from morning well into evening.
A few things stretch that further: pre-chill the flask with cold water before filling, fill it to the top (less air space holds temperature better), add ice, and keep the lid sealed between sips. Each time you open it, you let some heat in. With those habits, ice can last a remarkably long time inside a good flask. More in how vacuum flasks work.
Try the Steely vacuum flask.