Like almost any decent bit of outdoor kit, a good vacuum flask should also be robust and durable. All the flasks we tested are made of high-quality 18/8 food-grade stainless steel that resists dents, dings and scratches. The trade-off with steel flasks is that they can be heavy, although modern designs are shaving weight all the time, and in some cases, they now weigh little more than a standard plastic drinks bottle. Key attributes: Leakproof, practical design enables one-handed drinking, wide mouth for easy filling and cleaning Button-operated lids are more efficient to use than twist-and-pour stoppers – we found the button-operated lids to be more secure than the twist-and-pour stoppers. A solid performer in testing, SHO’s food flask kept water chilled for the advertised 20 hours and even managed to keep a portion of ice cream very cold, albeit a little melted, for the same period of time. Similarly, it kept hot food such as pasta piping hot over a period of 10 hours. The flask’s design also proved practical as well as stylish, with neat touches including a handy foldable spork, which stores in its lid, and a rubber carry handle. While the 530ml version is suitable for single portions, those of you looking to share may want to opt for the more roomy 800ml option. When single-use plastics started getting a bad rap, S’well became the drinks bottle of choice for a host of celebrities and ‘influencers’. But they’re not all style over substance – the design consists of a triple-walled construction incorporating a copper layer for improved insulation. This flask is lightweight and practical – the ergonomic shape makes it easy to hold, the really wide mouth makes for easy drinking, filling and cleaning, and the grooved lid makes it easy to open, even if screwed on tightly. It’s sure to draw admiring glances if you leave it on your desk at the office. It’s just a shame that the capacity is a bit small, and it’s relatively expensive for a little flask. Full Specifications

HOT OR COLD FOR 24 HOURS: Fill the 1L thermal flask with water, coffee, tea or other drinks, whether you're at home, work or outdoors; The double-wall vacuum insulation of this thermos keeps all your drinks hot/cold for 24 hours and 120 hours with ice Flasks are more 'smell prone' than 'stain prone' – none of the flasks we tested had any staining after cleaning, but some retained a faint coffee smell. To get maximum performance from your flask, you should always pre-warm it before use. Fill it with boiling water and leave to stand for five minutes or so before emptying and refilling with your chosen brew – such as tea, coffee, soup or hot chocolate. Filling your flask right to the top will also help minimise heat loss. Temperature Test: MethodCapacity: 500ml / Temperature test: 0 hrs 90°c, 90 mins 89.3°c, 4 hrs 82.8°c, 6 hrs 79.2°c, 8 hrs 75.3°c, 24 hrs 50.9°c / Stainless steel interior and exterior / Cool-touch, no-slip finish / Protective silicone rings for ultimate durability / Two part stopper for smooth pouring. BUY NOW: THERMOS.CO.UK

The original and, judging from the results of our temperature test, still the best. This stainless steel flask is very durable, with a silicone base to protect against dents. The two-part stopper closes securely yet pours easily and has an integrated cup. In terms of outright heat-holding performance for up to 8 hours, nothing can touch the Ultimate Series. It was the best-performing flask we tested overall. It is relatively lightweight too. And if you’re concerned that the 500ml capacity will be too small, it’s worth noting that Thermos also makes a larger 900ml version. Full Specifications Capacity: 600ml (20.3oz) / Temperature test: 0 hrs 90°c, 90 mins 79.6°c, 4 hrs 66.5°c, 6 hrs 58.3°c, 8 hrs 51.6°c, 24 hrs 22.2°c / Stainless steel construction / Wide mouth opening /It’s 100% leak proof – no matter how hard we tried, we couldn’t get any liquid to escape and the automatic opening trigger means you can drink from it one-handed with ease. Finally, there’s an additional loop handle on top so it can easily be attached to bags or simply carried this way. All in all, this is brilliantly stylish and robust Other useful design features to look for include a wide mouth, which makes for easier cleaning and filling (especially if you want to add ice cubes to your flask). In addition, many larger flasks incorporate ‘twist and pour’ spouts, so you can pour from the flask without having to completely remove the stopper. An integrated cup is also useful. Smaller flasks often feature lid designs that allow on-the-go swigging or one-handed operation. Multi-wall insulation: Double-wall insulation creates a vacuumed layer, which is vital for keeping hot drinks hot and cold drinks cold. Some flasks include more layers for even better insulation. The 100% stainless steel construction of today’s flasks means there’s no risk of inner walls shattering when dropped. EXTREMELY DURABLE: Our leak-proof thermos bottle has withstood speeding bullets, 4000 ft drops and category 5 hurricanes; The iconic style and rugged durability of this insulated bottle means it’s made to go anywhere

Since the American manufacturer, Thermos, came to fame, the term has become slang for vacuum-insulated flasks. Although the terms are largely interchangeable, the original scientific phrasing is 'vacuum flask'. Capacity: Bigger capacity means more contents to enjoy. It also means more weight to carry, but only if you fill it to the brim. For best insulation, buy a flask that’s slightly bigger (but not heavier) than you need, and leave a couple of centimetres of air at the top. We’ve included capacity and weight info for all our flasks below.

S’well Roamer 64oz Flask

A Thermos King will last years but it’s not officially dishwasher-safe, and you’re not even meant to submerge it in water (if you do, you kill the manufacturer’s 50-year guarantee). Inquisitive users report that it does survive the dishwasher intact, albeit with peeling colour. Capacity: 1 litre (33.8oz) / Temperature test: 0 hrs 90°c, 90 mins 86.5°c, 4 hrs 81.6°c, 6 hrs 78.1°c, 8 hrs 74.7°c, 24 hrs 53.7°c / Plastic-free stainless steel and silicone construction / 18/8 food-grade stainless steel interior doesn’t retain or impart flavours / Integrated double-wall construction cup / Twist and pour cap with 360° pour-through design / Internal Thread Design for increased thermal performance / Durable Klean Coat finish. BUY NOW: KLEANKANTEEN.CO.UK We’ve reviewed a selection of the best thermos flasks, ranging in size from 470ml to a whopping 64oz (1.8 litres). Bigger flasks usually retain heat better than smaller flasks, but are typically bulkier and heavier. We’ve compared their performance with our own temperature test. What Is The Best Thermos Flask?

We hand-washed each flask with hot soapy water and let them air dry overnight, then ranked them on smell. None of the flasks leaked from the main body – however, some flasks can't be filled to their stated capacity without liquid coming out when you screw on the lid. Textured coatings are useful – it’s a nice touch to have a handle on a drinks flask but generally, for a one-litre flask, it’s more useful to have a textured coating that provides grip. verifyErrors }}{{ message }}{{ /verifyErrors }}{{ Key attributes: Very light, design enables one-handed drinking, wide mouth for easy filling and cleaning.Capacity: 1 litre (33oz) / Temperature test: 0 hrs 90°c, 90 mins 85.5°c, 4 hrs 79.1°c, 6 hrs 74.3°c, 8 hrs 69.9°c, 24 hrs 44.5°c / Made of food grade 18/8 stainless steel that doesn’t impart or retain flavour / Lid doubles as a mug ensuring you always have a cup handy / Silicon sleeve / Drinking stopper opens and closes with a slight turn / Additional standard stopper for optimum heat retention included / Tapered design for easier handling / Large mouth opening is easy to fill and clean. BUY NOW: PRIMUSEQUIPMENT.COM