Insulated cup: Good flasks also pay attention to the insulation of the detachable cup, if they have one. This is so your drink stays warm while you’re drinking it. Meanwhile, the outside stays cool, so you don’t risk burnt hands. Capacity: 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 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 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

We dropped each flask five times from 90cm to mimic a dropped flask. Those with large dents that inhibited function or ability were rated low. 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 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 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. This flask has a familiar design with a classic ‘pop’ stopper that makes for easy pouring. With cheap, inferior flasks these are often prone to leaking but with this Outwell version the component seems well-made and reliable. It certainly didn’t leak on test. It’s a simple, inexpensive flask that makes use of a classic tried and tested design. The wide mouth makes the flask easy to fill and clean, while the cup’s plastic liner ensures you won’t burn your mouth. On the other hand, it is fairly bulky for a 750ml flask, with a small cup compared to some other designs. The external finish is also a bit slippery and prone to scratching. Full Specifications

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. 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.

Capacity: 592ml/20oz / Temperature test: 0 hrs 90°c, 90 mins 81.7°c, 4 hrs 72.4°c, 6 hrs 65.1°c, 8 hrs 59.9°c, 24 hrs 36.2°c / Double wall vacuum stainless steel construction / Screw in stopper with leakproof flip top lid / Powder coat finish / BPA-free and phthalate-free / Dishwasher safe (hand wash recommended). BUY NOW: EARTHWELL.COMTextured 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. 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.

Key attributes: Leakproof, practical design enables one-handed drinking, wide mouth for easy filling and cleaning 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'. BUILT FOR LIFE: ‘Built for life’ is a motto Stanley stood by since 1913 with their promise to provide rugged, capable gear, built to last a lifetime; If your Stanley doesn't life up its legendary reputation we'll do what it takes to make it right

Outwell Wilbur Vacuum Flask M

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.