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. Another advantage of stainless steel it that does not leave a metallic taste in the mouth or residual odours. However, it is always worth cleaning your flask thoroughly with hot soapy water between uses.

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.UK 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. 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 The temperature performance is excellent and compares favourably to the other top performers in the world of elite flasks. Your coffee will remain hot after 12 hours and your ice cubes will remain unmelted after a very decent 24 hours. So, you can still pour a chilled drink even after a long walk on a hot day. Part of this ability is due to the clever ‘honeycomb’ insulation used inside the Hydro Flask. It worked well for us! You can leave your house with a full bottle of coffee on Friday evening and can have a nice walk with a cup of hot coffee on your weekend destination even on Saturday evening! You will definitely get a duration of 24 hours, and this model performs equally well for hot and cold temperature contents. In Use

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 flasks

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.

Preview

Made in Australia this Decor 1 Litre flask has been made in olive to suit military use and is exclusively available through Platatac and its retailers. Avoid abrasive detergents and materials when cleaning your flask – bleach will stain and damage stainless steel, and scouring pads will scratch the outside of your flask 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. 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! 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.

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. Delivered Monday to Saturday 8am-8pm, excluding bank holidays. Once despatched you will receive updates from the courier. Slurping soup is great fun from the Milu – in fact, we’ve started using it at home because it keeps your minestrone piping hot, unlike a cold china bowl from the cupboard. 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. 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

That being said, we found that performance was not quite as good as a dedicated drinks flask – the Milu will keep your hot drinks hot for six hours and the cold ones for 10 hours. Glass-lined flasks are more dangerous because glass walls can also shatter To be safe, it's best to empty the contents after 24 hours. The flask has a BPA-free cup with enough space for several decent-sized cups of teas. The cup also helps ensure the flask remains leak proof. The Milu Thermo Food Flask is a bowl-shape flask (16 x 10 cm) that is not only useful for keeping your drinks hot/cold, but also certain types of liquid-based food. You can keep soup, rice, noodles, fruits and even baby food in this great flask. All parents know that it’s often a problem carrying baby food at the right temperature. The 450ml flask Milu is a great solution to the problem. Capacity: 750ml (25oz) / Temperature test: 0 hrs 90°c, 90 mins 85.2°c, 4 hrs 79.5°c, 6 hrs 75.3°c, 8 hrs 71.4°c, 24 hrs 48.4°c / Made from 18/8 stainless steel / Leak-proof / Insulated lid doubles as a cup / Dishwasher safe / Lifetime warranty.

We examined each flask and its pouring mechanism and attachments for faults. We penalised flasks that had faults affecting their usability.

S’well Traveler 16oz

Nothing beats a hot brew when you’re tramping around the hills on a winter hike. It’s like we’re hard-wired to appreciate that soothing warmth spreading around our bodies like a “Ready Brek” glow. 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.