It has been utterly brilliant. It keeps my coffee roasting hot, even on a trip up Narnain and Ime on a snowy day when wind chill was (apparently) making it feel like -20c! Some thermos flasks use a cork or plug to seal the liquid in, but we really don’t feel this is an effective design. Our suggestion is to go with a screw cap and a clip-on outer cap which will double as a cup. The downside of this approach is that a high capacity flask will be big and bulky. There’s no getting away from it. However, if you’re able to split your gear equally between all members of the team (e.g. one walker carries lunch, another carries the picnic blanket etc) then overall you will use less space than if you each carried smaller flasks. Warranty: We always suggest buying a vacuum flask from a manufacturer who will offer a warranty of at least one year, and preferably more. A warranty acts as a safeguard for your flask against unexpected defects, and ensures that you won’t have to buy again if something goes wrong. If you’re planning on spending a wodge of cash on a flask, then go for the one with the warranty. Typical Heat Retention Times

The Oneisall measures 34.5 x 11.5 x 11.5 cm and weighs 1.2kg. For a large capacity flask, those are not actually bad specifications. And it really does look the business! Beautiful lines as they say! For a group hike, you need to keep lots of liquid on board for everybody to get a cup. If this is your plan then you should buy a thermos which can hold lots of liquid for the whole squad. It is definitely more space efficient to use one big flask for the group rather than several small, individual flasks. If you think about it, the majority of a flask is wasted space and not actually used for carrying liquid – it is there for the heat insulation. Better to just carry one big flask.A range of scientific research has shown that BPA can seep into food or beverages and potentially cause a range of issues for the brains of fetuses, infants and children. Additional research suggests a possible link between BPA and increased blood pressure. The best thermos flasks can keep liquids hot or cold for a long time – over 12 hours in some cases. Look for a two-layer construction with an intermediate vacuum layer. This prevents heat loss by convection and conduction.

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 If you take your thermos flask to the local coffee shop and ask them to fill it up instead of having your drink served in a disposable coffee cup with plastic lid then you will be reducing the amount of landfill and waste material which gets produced from these establishments. Win win in our books! Why ‘Thermos’?

Available in a range of colours (we like the electric blue), the flask is highly suitable for camping trips and general travelling refreshments. Pouring is very easy due to the superb flexible handle fabricated from silicone. 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.

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 You may not have heard of ‘BPA’, but in a similar way to aluminium in camping kettles, it should be avoided when you’re looking for a thermos flask. BPA stands for Bisphenol A, and it’s a chemical which has been used to make certain plastics and resins since the 1960s, and was commonly found in thermos flasks. This is definitely one of the best thermos flasks for solo users due to the size of 21.8cm x 6.5cm and weight of only 0.33kg. This is light!