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. The GSI employs a thin but reliable stainless steel wall that reduces the weight and also increases the internal space of the bottle. According to GSI, you can store 25% more liquid than any other flask for the same size.

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. 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: Method In terms of tech, the Oneisall employs a copper-coated layer outside of the vacuum space which ensures that the flask keeps your drinks hot without any heat reaching the outer surface. Hydro Flask are a fashionable US company who have made reusable flasks and water bottles immensely cool over on the West Coast of America. The Hydro Flask Wide Mouth is a quality vacuum flask employing some great tech, a lovely powder-coated exterior surface for great grip as well as excellent heat retention properties. The downside is that they are a touch on the expensive side – you don’t get this sort of style for free girl!You can see that a thermos flask will be a great companion for any outdoor activity! Using a Thermos Flask is Environmentally Friendly 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

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. All materials on the Stanley are very robust and have a quality utilitarian feel to them. You can be assured that the food-grade stainless steel used on the Stanley won’t give a metallic taste to your drinks at all, but offers excellent heat retention.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

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. The temperature performance of the Smardy is quite praiseworthy. It gives around 12 hours for hot drinks and 24 hours for cold drinks. Certainly good enough for day trips in any conditions. We examined each flask and its pouring mechanism and attachments for faults. We penalised flasks that had faults affecting their usability.

MontiiCo Original Bottle

This thermos flask is made of a combination of Stainless Steel, Polypropylene and Silicone, and the dimensions are an excellent 21.1 x 12 x 9.1 cm. It is sized extraordinarily well for solo hikers who are concerned about size and weight but still wish to carry a hot brew around to warm up with. In our opinion this is one of the best thermos flasks on the market today. 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). The Okadi is a 2.5L flask which offers extremely good capacity for both family and group adventures. It is fabricated from stainless steel which gives excellent core strength and durability. This thermos will last for a long period of time indeed. The 18-8 flask is from the renowned brand Stanley. Stanley has been serving people since 1913 and this model is truly legendary. No other brand apart from Thermos themselves can boast such heritage. Dimensions