HOW A VACUUM FLASK WORKS
A vacuum flask, or thermos, does not allow heat transfer by any of the three ways that heat can travel.
The silver coating on the inner bottle prevents heat transfer by radiation, and the vacuum between its double wall prevents heat moving by convection.
The thinness of the glass walls stops heat entering or leaving the flask by conduction. The case surrounding the flask provides additional insulation.
Vacuum flasks have come a long way since the thick plastic mugs of your childhood. Easy-to-clean materials and impenetrable insulation are now standard features of the best vacuum flasks. But, despite all of the cool new features out there, not all vacuum flasks are created equal.
When you’re looking for your ideal vacuum flask, you need to consider which features you need the most. If you usually carry cold drinks, look for a double-walled bottle. The extra insulation keeps the bottle from sweating, so you won’t end up getting drips of water all over the place.
If you use a travel mug mostly for coffee, a tight seal is your best bet. Vacuum seals prevent the lid from popping open and spilling hot coffee everywhere, and they also trap the heat inside the bottle — so your coffee will stay hot for hours. You can even carry some homemade soup that’ll stay warm till lunchtime.
If you like to have different drinks in your travel mug every day, that’s fine, too! Most of these vacuum flasks can deal with hot or cold. The insulated walls leave them cool to the touch, so you’d hardly know if you were carrying around ice cold water or boiling hot tea.
These vacuum flasks make daily hydration hydration (and caffeination) a million times easier — and many of them are BPA-free and dishwasher safe.
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