The two glass-lined flasks we tested were the only flasks to fail our drop test: one shattered on the first drop, the other fell apart on the second. 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'. Need to know: Not dishwasher safe, twist-off lid, glass and plastic materials, comes with two cups, also available in 1.8-litre size

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. 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 Don't leave food and drink in a flask for a long period of time Bacteria can breed and this produces gas. Pressure then builds up which can force the lid off the flask.Heat and cold retention is exemplary, with the Thermos lasting well over 24 hours for both. We found that it is particularly effective for cold drinks, with ice cubes still being solid after a 30 hour test we performed. Thermos have obviously squeezed out all routes for heat to get into the inner chamber of the flask.

Don't fully submerge the flask in water – doing this might allow water to get inside the insulation layers, affecting the quality of insulation You can see that a thermos flask will be a great companion for any outdoor activity! Using a Thermos Flask is Environmentally Friendly 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. Textured coatings are useful – it’s a nice touch to have a handle on a drinks flask but generally, for a one-litre flask, it’s more useful to have a textured coating that provides grip. Other useful design features to look for include a wide mouth, which makes for easier cleaning and filling (especially if you want to add ice cubes to your flask). In addition, many larger flasks incorporate ‘twist and pour’ spouts, so you can pour from the flask without having to completely remove the stopper. An integrated cup is also useful. Smaller flasks often feature lid designs that allow on-the-go swigging or one-handed operation.

Thermos should just rename their 1 litre ‘Light and Compact’ vacuum flask as “The Daddy” because it effortlessly delivers everything you would expect from the company who developed the vacuum flask as we know it today from Sir James Dewar’s original prototype in 1904. 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. You may think choosing a vacuum flask is a simple matter of grabbing the shiniest example in the camping shop (if it’s open!) and hoping for the best. Well, unfortunately we’ve tried that approach several times and have frequently been disappointed. We’ve reviewed a selection of the best thermos flasks, ranging in size from 470ml to a whopping 64oz (1.8 litres). Bigger flasks usually retain heat better than smaller flasks, but are typically bulkier and heavier. We’ve compared their performance with our own temperature test. What Is The Best Thermos Flask?

Invest in a sturdy bottle brush for stainless steel flasks – it will help you get to hard-to-reach areas inside the flask but could damage glass-lined flasksIf 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’? If you’re after a large flask, the Oneisall 2L is a great stainless steel option with a lovely ergonomic design. This is a high-quality two litre flask which is capable of serving drinks for the whole family – great to bring along for day trips in the car or campervan.