You can also keep liquids cooler on hot sunny days in a metal water bottle compared to a plastic one. The weight difference is marginal between a 40oz wide mouth Klean Kanteen and a Nalgene bottle i.e only a few oz difference. Wrapping the bottle in a wet hand towel such as Lifeventure soft fibre hand towel

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then placing in a mesh bag will form an evaporative cooling system to keep the metal bottle contents cold on a warm sunny day along the same principle as this;

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