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). My hot water was 93.6°C at 8:25pm, and I already had my suspicions, because the exterior was markedly hot compared to the others – a sure sign of heat escaping. At 8:25am it was 34.8°C – a significant temperature drop of 58.8°C after 12 hours. Unlike the other flasks, my cold water and cubes didn’t get colder – it got hotter. The marketing blurb says it keeps contents hot for 28 hours, or cold for 90 hours, which based on these results I can’t really see happening. 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). My hot water was 91.3°C at 8:36pm; at 8:36am it was 75.7°C – a temperature drop of 15.6°C after 12 hours (not that much more than the Stanley, and still piping hot enough for a decent brew). My cold water was 4.4°C at 11:13am, and as with the Stanley, 12 hours later it was even colder – at 1.7 °C. 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).

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. One of its aims is to reduce the amount of plastic going into the ocean by encouraging the use of a steel bottle, so it is proudly 100pc BPA free.If you want to carry your flask long distances, it’s a lightweight option – weighing 400g (14 ounces) with canteen cap, or 380g (13.4 ounces) with sports cap, while empty. You probably wouldn't describe the scientific rigour as laboratory standard – but the tests did replicate the kind of environment you'd actually use these flasks in, either filling up your tea or coffee at the start of the day, or icing water. And the results were certainly interesting. While the cold water tended to record similar temperatures across products (with the exception of Klean Kanteen, which I'll get to), there was a significant degree of difference when it came to heat retention. My conclusion is that if you really care about keeping your caffeine hot, you should choose your insulated flask wisely. verifyErrors }}{{ message }}{{ /verifyErrors }}{{ The wide mouth means it’s also suitable for soups and smoothies to take to work, and it will certainly keep them either sufficiently cold or hot until lunchtime. It's available in a range of colours, which is fun, from canary yellow to baby blue via three shades of pink.

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. 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. 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.

Red Paddle Co manufacture paddle boards, but now they’ve also launched a versatile equipment range, Red Original. The kit can be used by anyone (no paddling required) and their marine-grade stainless steel water bottle is cleverly designed. The higher quality steel means it doesn’t corrode like other metal drinks bottles, and can withstand the elements. My hot water was 92.3°C at 8:05pm, and by 8:05am it was 57°C – a temperature drop of 35.3°C after 12 hours. It’s still “warm” – just not as warm; and certainly not pipingly hot. My cold water with ice cubes is 5°C at 11:02 and 12 hours later its 3.5°C. The Stanley Classic is the Daddy of all insulated flasks, and with good reason. My hot water was 84.6°C at 7:51pm, and at 7:51 am it was 70.8 °C – a temperature drop of a mere 13.8°C after 12 hours (far less than its competitors, as detailed below). 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.