A vacuum flask water bottle, commonly referred to as a thermos, is designed to keep liquids either hot or cold for long durations. The technology behind this lies in the vacuum insulation – a double-walled construction with a vacuum in between, which significantly reduces heat transfer. https://medium.com/@clonko/vacuum-flask-water-bottle-the-perfect-companion-for-temperature-control-on-the-go-03dde62b965c