We hand-washed each flask with hot soapy water and let them air dry overnight, then ranked them on smell. 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: 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 / To help you choose which one to invest in, I tried and tested a selection of flasks that promise to keep your beverages colder and hotter for longer, measuring how much heat was retained or how cool they kept respectively over a period of 12 hours.

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. Unlike many flasks, it is also dishwasher safe – a big bonus in my book. The lid doubles up as a decent-sized cup and provides extra insulation; a handle on the side makes it easy to lug around and grip while battling the elements, but there’s no chance of leakage. While primarily made up of stainless steel, some parts are plastic – but it is BPA-free (an industrial chemical used in water bottles and similar that many people prefer to avoid). How do Thermos flasks work? In short, they use a double walled construction, with the air removed from between these walls, forming a vacuum. Heat struggles to pass through the vacuum, meaning liquid stays at a roughly constant temperature. YOUR INEXPENDABLE COMPANION AT ALL TIMES - The practical KAAVE vacuum flask for on the go, at home, in the office or outdoors. Highly durable thanks to the sturdy handle and bottom. A reliable companion that guides you through the day. Perfect for every tea and coffee enthusiast -Ideal for sharing thanks to 2 cups integrated into the lid - because sharing is caring. 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.KAAVE THERMO SHIELD | 24h Hot / 36h Cold - Outstanding insulating properties of the highest level due to the copper coating in the double-wall vacuum design. Always THE PERFECT TEMPERATURE all day long. 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.

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.UKCapacity: 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 FUNCTIONAL DESIGN + CLEVER ENGINEERING - The body is entirely made of high-quality 304 food safe stainless steel - Incredible capacity of 1000 ml ensures sufficient volume for long days. The cups are a joy to hold in the hand thanks to the ergonomic handle. Dimensions: Body Ø 11 cm x 30.8 cm height. Weight: 790g. A big part of the appeal of the Stanley is that it makes you feel like an intrepid camper, thanks to the distinctive green branding. With a lifetime warranty, the iconic flask will survive even the wildest of adventures: since it was founded in 1913, Stanley bottles have survived -70 degree winds, 4,000 foot drops, speeding bullets and category 5 hurricanes (please do not try this yourself).

It comes with two cups with proper handles, so it's a great tea flask. It works well for families and small groups, making 5 or so generous servings. The twist stopper has a cunning hidden compartment in which to store milk or sugar; which I liked. 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.UKKey attributes: Very light, design enables one-handed drinking, wide mouth for easy filling and cleaning. Key attributes: Leakproof, practical design enables one-handed drinking, wide mouth for easy filling and cleaning

So, whether you're planning on travelling the world or exploring closer to home, we have what you need for your next ADVENTURE. Similarly to the likes of the Stanley, I like the aesthetic, and it also has a double wall construction to create a vacuum between the outside environment and inside liquid, helping to keep cold drinks cold or hot. The 750ml capacity holds around three cups of hot coffee (or the equivalent of a chilled bottle of white wine). Or even What are the Top 10 affordable (best budget, best cheap, or even best expensive!!!) 2 Cup Thermos Flask available? Etc. We examined each flask and its pouring mechanism and attachments for faults. We penalised flasks that had faults affecting their usability.After Stanley, I found the Thermos – a brand which has become synonymous with insulated flasks – to come a close second in terms of heat retention. However, it is durable and robust and does come with a lifetime warranty. It weighs 723g, and if the environment is your number one priority, it’s still functional enough. Happy camping.