In autumn the flask moves from the cupboard back into the rucksack: for walks, hikes, fishing, the car or just the working day. They all look almost the same, but one keeps tea hot until evening while another goes cold by lunchtime and leaks in your bag. Here is what to look for when choosing, plus seven popular models from AliExpress.
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How a vacuum flask works and what “keeps heat” means
The key to a flask is a double-walled inner bottle with a vacuum between the walls. A vacuum hardly conducts heat, so a hot drink cools slowly and a cold one warms up just as slowly. If the vacuum is broken, for example by a hard knock that leaves a dent, the flask turns into an ordinary metal bottle.
A good benchmark comes from the Vietnamese manufacturer Rang Dong: in a quality flask a hot drink should lose no more than 4 degrees in 6 hours and no more than 6 degrees in 12 hours, while a cold drink should stay cold for a day. The Swedish chain Biltema says a coffee flask keeps coffee hot for roughly 6 to 8 hours. Cheap models usually sit closer to the second figure, which is plenty for a walk or a working day.
What to look for when choosing
Type: bottle, mug or food flask
A classic flask with a stopper and cup lid is the one to get when several people will drink from it. A travel mug is handy in the car and in town: you can open it with one hand and drink on the move. A food flask with a wide mouth is made for soup, porridge and main dishes, and pouring tea into it is awkward. Biltema specifically advises choosing a food flask for meals.
Capacity
For one person for a day, 350 to 500 ml is enough, and for two about a litre. Rang Dong counts flasks up to 1 litre as personal. Anything over 1.5 to 2 litres makes sense for fishing, the car or a group: on a long hike every extra gram is felt on your shoulders.
Inner bottle material
The inner bottle should be food-grade stainless steel, grade 304 or 316, both of which are described as corrosion resistant. Grade 316 costs more and copes better with salt and acid. Glass inners hold heat well and add no taste, but they break easily, so they are usually left at home when hiking or travelling by car. Steel, as Biltema notes, also stands up reliably to frost.
Lid and leak-proofing
The lid is most often the weak point. A good stopper screws in tightly and has a silicone ring that can be removed and washed. If the flask will lie flat in a rucksack, look for the word “leak-proof” in the description and always test it at home: fill it with water, turn it upside down and leave it for a few minutes.
Extra features
A temperature display on the lid is handy if you pour hot tea for children: you can see when the drink has cooled to a comfortable level. A straw and a handle are more for sports bottles, and a classic tea flask is simpler without them.
Popular models from AliExpress
TYESO flask
The best-selling flask in our selection, at £8.59. It has a stainless steel vacuum inner bottle and suits the car, time outdoors and trips. TYESO is one of the best-known names among flasks on AliExpress.
Price on 22 October: £8.59
Sold: 3767+ pcs, positive reviews: 97.2%
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304 steel bottle with straw
A sports bottle with a 304 stainless steel inner, suitable for hot and cold drinks. It costs £10.29. The straw is handy in the gym and on a bike, but for hot tea it is better to take it off.
Price on 22 October: £10.29
Sold: 3471+ pcs, positive reviews: 98.0%
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Thermo Cafe travel mug, 380 or 510 ml
A leak-proof travel mug with double stainless steel walls, in a choice of two sizes, for £4.39. A good option for the car and the commute.
Price on 22 October: £4.39
Sold: 2843+ pcs, positive reviews: 98.0%
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Mini flask, 200 or 360 ml
A pocket flask that fits in a jacket pocket or a small bag, at £4.69. It suits a single portion of coffee on a walk, or a child’s school bag.
Price on 22 October: £4.69
Sold: 1749+ pcs, positive reviews: 98.0%
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SoftAura with temperature display
An SUS304 steel inner and an LED temperature display on the lid, for £7.76. The size is your choice, from 500 ml to 1 litre. Useful if you want to see how hot the drink is without opening the flask.
Price on 22 October: £7.76
Sold: 1449+ pcs, positive reviews: 98.0%
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Food flask, 630 or 1000 ml
A double-walled, vacuum-insulated jar for soup, porridge and other hot meals, at £7.69. The wide mouth is easy to wash and to eat from directly.
Price on 22 October: £7.69
Sold: 996+ pcs, positive reviews: 98.0%
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2-litre 316 steel flask
The biggest option in the selection, at £19.39, with a 316 steel inner, a straw and a handle. It suits camping, fishing and group trips, when one litre is not enough.
Price on 22 October: £19.39
Sold: 1450+ pcs, positive reviews: 98.0%
View on AliExpress
How to look after a flask so it lasts
- Rinse it before first use with warm water and washing-up liquid to remove the factory smell.
- Preheat the inner bottle. Pour in boiling water for a couple of minutes and empty it, and the drink will then cool noticeably more slowly.
- Wash it after every use with a brush and washing-up liquid, especially after tea and coffee.
- Dry it open. Rang Dong advises storing the bottle completely dry, or a smell will develop.
- Do not leave it for long in a hot car or next to a heater: constant heat can damage the vacuum insulation.
- Replace the flask if rust or dents appear, or if the drink stops holding its temperature as it used to.
Verdict
For all-day tea and trips, take a classic flask or bottle of 500 to 750 ml, a travel mug for the car and town, and a wide-mouth food flask for lunch. For groups and fishing, a 2-litre model will do. And whichever flask you choose, the first thing to do is test it for leaks at home.
