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. Another advantage of stainless steel it that does not leave a metallic taste in the mouth or residual odours. However, it is always worth cleaning your flask thoroughly with hot soapy water between uses. 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 / 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.

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'. 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. 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

Key attributes: Very light, design enables one-handed drinking, wide mouth for easy filling and cleaning.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 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. Key attributes: Leakproof, practical design enables one-handed drinking, wide mouth for easy filling and cleaning 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.