Nothing beats a hot brew on a chilly day in the hills, and the best way to keep your tea, coffee or soup steaming hot is by packing a good thermos flask in your rucksack. All insulated flasks work on the same basic principle. They use a double-wall construction, separated by an airless cavity, which creates a thermal insulation layer that keeps liquids hot for longer. The same vacuum principle applies to keeping drinks cold, so double-walled flasks are also a great way to keep drinks ice-cold on a hot hiking day. We’ve a selection of the best thermos flasks, ranging in size from 470ml to 1 litre. Bigger flasks always retain heat better than smaller flasks, but are typically bulkier and heavier.
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