PACKING HEAT

Lois Borny on the top-rated flasks and insulated mugs

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A good flask makes all the difference. Whether you're facing a chilly winter commute or a hot and humid summer walk, having a flask that actually works is a small but satisfying win.

The best can keep your drink at the optimum temperature for hours - some can even maintain it at the tastiest temperature for an entire day. The market is packed with options, whether you need something the size of a coffee cup for the office or a massive tankard for a cosy cup of tea while camping.

After lots of testing, I've assessed not just the best brands, but the best styles for different needs. For longer excursions, opt for built-in cups like those from Klean Kanteen and Thermos, and mouthpieces that allow quick, drip-free, and sometimes onehanded sips for when you're on the go, such as the push-to-open design of Contingo's flask. Flasks aren't just for holding water or a brew - I've even tested a flask specifically designed for holding a bottle of wine. It's perfect for picnics.

Ultimately, what makes a flask worth your money is its ability to slow down heat transfer - either in or out - via a layer of almost airless space sandwiched between the flask's inner and outer walls.

Keep reading to find out which flasks impressed me the most.

How I tested

First and foremost, flasks had to keep drinks hot or cold to make it onto my list. I assessed the brands' claims by filling the flasks with boiled and iced water, then drinking from them hours later to see if the temperature held.

• Ease of use: I used each flask in different situations, like at my desk, on a walk, and sitting at home, to see how straightforward they were to open, drink from, and close again.

• Mouthpieces: I tested the mouthpieces by drinking from them repeatedly throughout the day, paying attention to how comfortable they felt, whether the flow was smooth, and if it was easy to clean.