While Thermos may be a well-known and generic term for a flask, it’s just one of many brands. In fact, the best flasks come in all shapes and sizes and under many names. Our recommendations below have managed to master the art and science of the vacuum flask – that ingenious, insulated container that does the job of a portable kettle or fridge without the need for a plug socket.
Whether it’s a chunky “food flask”, sleek “vacuum bottle” or something in between, the job of a flask is to keep food and drink hot or cold without leaking, all day long. Some of the winners on our list can insulate for more than 24 hours, which is long enough to survive the toughest hike or most gruelling commute. Electric Cool Bag
For this article, we’ve picked out several flasks that excel at insulation, leak-proofness, durability and, of course, value for money. Before you scroll on, take a look at our buying guide below for some helpful tips on buying the best flask.
Flasks have come a long way and today’s best vacuum flasks are mini engineering marvels. Made from multiple layers of BPA-free and rust-proof stainless steel, these flasks should survive years of bumps and knocks, keeping you in hot cuppas and ice-cold drinks season after season.
They also win big on green points, doing away with the need to buy drinks in single-use cups. If your flask is big enough for lunch you can save on both money and plastic.
READ NEXT: The best energy drinks for a midday boost
You can buy flasks for next to nothing but, given how often you’re likely to use your flask, it’s worth spending a bit more for quality and durability.
You tend to get what you pay for when buying vacuum flasks. Of course, you can get flashy designer flasks, but if you’re looking for quality alone you won’t have to spend more than about £25-£30. That may seem extravagant for a drinks container, but you will soon save much more on drinks and lunches.
18/8-grade steel: Today’s best flasks are made from stainless steel that doesn’t secrete chemicals (they’re BPA-free, in other words) or weird flavours. The best of the best are made from 18/8-grade steel (aka 304-grade), whose high nickel content makes it rust-proof and extremely durable. It’s also non-magnetic, which may disappoint if you would hoped to adorn your Thermos with fridge magnets.
Multi-wall insulation: Double-wall insulation creates a vacuumed layer, which is vital for keeping hot drinks hot and cold drinks cold. Some flasks include more layers for even better insulation. The 100% stainless steel construction of today’s flasks means there’s no risk of inner walls shattering when dropped.
Insulated cup: Good flasks also pay attention to the insulation of the detachable cup, if they have one. This is so your drink stays warm while you’re drinking it. Meanwhile, the outside stays cool, so you don’t risk burnt hands.
Capacity: Bigger capacity means more contents to enjoy. It also means more weight to carry, but only if you fill it to the brim. For best insulation, buy a flask that’s slightly bigger (but not heavier) than you need, and leave a couple of centimetres of air at the top. We’ve included capacity and weight info for all our flasks below.
READ NEXT: Best reusable coffee cups
Price when reviewed: £20 | Check price John Lewis
At the other end of the weight spectrum comes this gorgeous newcomer from Thermos, weighing in at barely more than 200g (before there’s anything in it, of course) and topped with a ‘direct drink’ spout that’s perfect for the train to work.
Thermos designed the flask to be as light and ergonomically comfortable as possible, with a cool sweat-proof exterior. It can’t match the Stanley Master for sheer insulating power (no flask can, to be honest) but it still does a great job of keeping cold drinks cold for a couple of days, and hot drinks piping hot all day.
Key specs – Material: Stainless steel (not officially dishwasher-safe); Capacity: 470ml; Size: 22 x 6.5 x 6.5cm; Weight: 210g; Colours available: 1
Price when reviewed: £35 | Check price at AmazonKeep drinks cold in the blazing sunshine with this stylish, lightweight, double-wall insulated bottle, made from sturdy stainless steel and a powder-coating finish to stop it slipping out of sweaty hands. It does keep hot drinks hot for 12 hours, but it’s on summer adventures that this flask really comes into its own, keeping iced drinks cold for more than 24 hours.
Hydro Flask also comes in a smaller 12oz version and in a ‘wide mouth’ design, but only the standard mouth fits the insulated silicone Sport Cap (£10), designed for taking generous sips on the go.
Key specs – Material: 18/8 stainless steel (dishwasher-safe); Capacity: 600ml; Size: 26.5 x 7.3 x 7.3cm; Weight: 295g; Colours available: 3 (more colours available from other retailers)
Price when reviewed: £26 | Check price at AmazonDrop it, dent it, dishwash it, drink straight from it, even brew tea in it. This fab lightweight flask is designed to survive anything, without messing with the temperature of its contents, keeping your brew comfortably hot for 12 hours.
The two-part locking lid doubles as a rotatable spout, so it’s ideal for taking a sip when you’re walking, although the plastic part of the lid does feel somewhat less durable than the metal. We also love the classic Sigg handle, which doubles as a lever so you can open it using a stick if your hands are cold or dirty. There’s even a built-in tea filter, so you can make tea using loose tea leaves or whatever you find on your adventures.
Key specs – Material: 18/8 stainless steel with polypropylene strainer (dishwasher-safe); Capacity: 500ml; Size: 25.5 x 6.9 x 6.9cm; Weight: 381g; Colours available: 3 (silver, white, black)
Price when reviewed: £30 | Check price at John Lewis The Thermos King is surprisingly light given its size (it’s bigger than the Stanley Master but lighter and cheaper) and looks spectacular. Thoughtful details include a twist-and-pour stopper that lets you pour drinks without removing it, and a space-saving handle. However, it doesn’t insulate for as long as the Stanley Master, and it’s a bit drippy when pouring from the spout, at least when it’s full.
A Thermos King will last years but it’s not officially dishwasher-safe, and you’re not even meant to submerge it in water (if you do, you kill the manufacturer’s 50-year guarantee). Inquisitive users report that it does survive the dishwasher intact, albeit with peeling colour.
The pictured flask is in Cranberry Red; John Lewis also has it in Matt Forest Green (£30). More colours and sizes are available from Thermos.
Key specs – Material: 18/8 stainless steel (not dishwasher-safe); Capacity: 1.2l; Size: 31 x 10.5 x 9.4cm; Weight: 670g; Colours available: 2 (more colours available from other retailers)
Price when reviewed: £25 | Check price at John Lewis The King is back, and this time he’s full of lunch. Here, the Thermos’s insulated stainless steel lid doubles as a serving bowl, and comes with a full-size folding stainless steel spoon. Stews and soups stay very hot all day, while fruit and tubs of yoghurt stay cool all day – or fridge-cold if you include an ice pack in the flask. Ice cream won’t quite go the distance, but if you pack the flask with a handful of wrapped lollies straight from the fridge they’ll stay frozen for a few hours.
Key specs – Material: 18/8 stainless steel (not officially dishwasher-safe); Capacity: 470ml; Size: 14.2 x 9.4 x 9.4cm; Weight: 390g; Colours available: 2 (more colours available from other retailers)
Price when reviewed: From £20 | Check price at AmazonIf you’re looking for a food flask that eschews the usual rugged look in favour of something a little more sleek and stylish, the SHO food flask is the option for you. It comes in a wide range of colours, ranging from pastel matte options to fun gradient styles, making it a perfect camping or travel accessory for the style-conscious among us.
A solid performer in testing, SHO’s food flask kept water chilled for the advertised 20 hours and even managed to keep a portion of ice cream very cold, albeit a little melted, for the same period of time. Similarly, it kept hot food such as pasta piping hot over a period of 10 hours. The flask’s design also proved practical as well as stylish, with neat touches including a handy foldable spork, which stores in its lid, and a rubber carry handle. While the 530ml version is suitable for single portions, those of you looking to share may want to opt for the more roomy 800ml option.
Key specs – Material: 18/8 stainless steel (not officially dishwasher-safe); Capacity: 530ml, 800ml; Size: 10 x 10 x 17cm; Weight: 480g; Colours available: 18
Price when reviewed: £77 | Check price at Amazon New from the creators of the 106-year-old Stanley Classic, this sleek, rugged flask keeps hot drinks hot for longer than the promised 27 hours and iced drinks cold for a staggering 100+ hours (good luck if you’re caught out in a heatwave for that long, frankly). So if you’re packing the car for a camping trip, this is the flask to take.
The Master achieves its insulating magic with a “QuadVac” quadruple-walled insulation system, made entirely from BPA-free 18/8-grade rust-proof steel. The insulated cup is made from the same stuff, and does a brilliant job of retaining a drink’s temperature while you take your time over lunch. The stopper is plastic but lined with steel, so your drink never comes into contact with plastic, and we found it to be reliably leak-proof.
Our only grumble is that the flask weighs nearly a kilo even before there’s anything in it, and isn’t available in a smaller size.
Key specs – Material: 18/8 stainless steel with steel-lined plastic inner cap (dishwasher-safe); Capacity: 750ml; Size: 30 x 8.8 x 8.8cm; Weight: 889g; Colours available: 1
Price when reviewed: £26 | Check price at MilletsThis large, robust flask comes with a removable shoulder strap, so you could throw it over your shoulder while you’re heading up a mountain for the weekend. And if you’re heading out there with a friend, even better, because there’s a second plastic ‘buddy cup’ hidden inside the larger metal one. The flask is wide enough to be used as an insulated lunchbox, too, but you would need to bring your own spoon. Insulation is excellent, keeping contents piping hot for over 12 hours.
Key specs – Material: 18/8 stainless steel with copper coating (dishwasher-safe); Capacity: 1l; Size: 23 x 12 x 11.5cm; Weight: 708g; Colours available: 1
Price when reviewed: £25 | Check price at AmazonIf you’re not a big hot drink fan but still want an exceptional flask to keep drinks cool on camping trips, long days and overnight stays, this slick offering from travel favourite Contigo is ideal. It claims to keep drinks cold for 28 hours and during our testing, it lived up to this. While the temperature will drop a tad when ice begins to melt, we found that iceless liquids were the same temperature 28 hours later as they were when first added. In some instances, they stayed chilly for far longer than the time stated too.
It’s 100% leak proof – no matter how hard we tried, we couldn’t get any liquid to escape and the automatic opening trigger means you can drink from it one-handed with ease. Finally, there’s an additional loop handle on top so it can easily be attached to bags or simply carried this way. All in all, this is brilliantly stylish and robust
Key specs – Material: stainless steel (plastic lid dishwasher safe) Capacity: 720ml; Size: 7.6 x 7.6 x 27.4 cm; Weight: 382g; Colours available: 2
Price when reviewed: £28 | Check price at &Keep
This vacuum-insulated flask from Black+Blum is a highly distinctive and eco-friendly option for keeping your food nice and warm. It has a capacity of 400ml and its leak-proof twist lid ensures that food and drink stay put, wherever you go. Once sealed, it can keep food hot for up to six hours, while boiling water will stay piping for ten or more. Meanwhile, cold food and drink will keep their cool for roughly eight hours. Finally, that colourful, ergonomic spoon stays fixed to the flask by slotting into the artificial leather strap, so you will never end up drinking your soup like tea.
Key specs – Materials: 304 stainless steel, polypropylene, HIPS, silicone and artificial leather (not dishwasher/microwave-safe); Capacity: 400ml; Size: 16 x 9 x 9cm; Weight: 349g; Colours available: Ocean, Orange, Olive
Titan Lunch Bag Copyright © MVF Global 2023. All rights reserved. Expert Reviews™ is a registered trade mark.