A good flask makes all the difference. Whether you’re facing a chilly winter commute or a hot and humid summer walk, having a flask that actually works is a small but satisfying win.
The best can keep your drink at the optimum temperature for hours – some can even maintain it at the tastiest temperature for an entire day. The market is packed with options, whether you need something the size of a coffee cup for the office or a massive tankard for a cosy cup of tea while camping.
After lots of testing, I’ve assessed not just the best brands, but the best styles for different needs. For longer excursions, opt for built-in cups like those from Klean Kanteen and Thermos, and mouthpieces that allow quick, drip-free, and sometimes one-handed sips for when you’re on the go, such as the push-to-open design of Contingo’s flask. Flasks aren’t just for holding water or a brew – I’ve even tested a flask specifically designed for holding a bottle of wine. It’s perfect for picnics.
Ultimately, what makes a flask worth your money is its ability to slow down heat transfer – either in or out – via a layer of almost airless space sandwiched between the flask’s inner and outer walls.
Keep reading to find out which flasks impressed me the most.
How I tested
First and foremost, flasks had to keep drinks hot or cold to make it onto my list. I assessed the brands’ claims by filling the flasks with boiled and iced water, then drinking from them hours later to see if the temperature held.
- Ease of use: I used each flask in different situations, like at my desk, on a walk, and sitting at home, to see how straightforward they were to open, drink from, and close again.
- Mouthpieces: I tested the mouthpieces by drinking from them repeatedly throughout the day, paying attention to how comfortable they felt, whether the flow was smooth, and if it was easy to clean.
- Lids: I checked how easily each lid opened and closed, and did this several times to see how secure they were. I checked whether they snapped shut firmly and how quickly I could use them without fiddling around.
- Handles: I assessed each flask on how comfortable the handles were, if it had any. I carried them by the handles to see if they would still retain liquid (if sideways) and if it was uncomfortable to do so when the flasks were full.
- Leak-proof: For a travel flask or mug, this is one of the most important factors. I shook and tipped each one upside down after filling it to test if any liquid escaped, and also kept them in my bag to check for leaks during daily use.
- Temperature control: I filled the flask with hot tea and with iced water, leaving it for several hours to see how well it maintained the temperature. I also compared the first sip with the last to test consistency.
Why you can trust IndyBest reviews
Lois Borny has been part of the IndyBest team since 2021. She has written about household essentials (like vacuum cleaners), fashion, and a whole lot more in between. When testing items, Lois factors in quality, value for money and, ultimately, whether they're effective. Every flask on her list has been put to the test in the real world. If she doesn’t think a product is worth buying, it won't make the cut.
The best insulated flasks for 2025 are:
- Best overall – Thermos superlight drinks flask, 470ml: £17.56, Amazon.co.uk
- Best budget – Lifeventure TiV vacuum flask, 700ml: £22.99, Lifeventure.com
- Best for style – Stanley quencher H2.0 flowstate tumbler, 1.2l: £36.27, Amazon.co.uk
- Best insulated mug – Hydro Flask coffee mug, 354ml: £28.95, Amazon.co.uk
- Best hi-tech flask – Larq bottle purevis, 500ml: £89, Livelarq.com
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Thermos superlight drinks flask
Best: Flask overall
Material: 18/8 food grade stainless steel, BPA-free
Weight: 0.21kg
Capacity: 470ml
Max temperature preservation times: Hot for 10 hours, cold for 24 hours
Dishwasher safe: No
Why we love it
- Looks great
- Light and compact
Take note
- Not everyone will like the mouthpiece for hot drinks
There’s so much to like about this little flask from Thermos. On first impressions, it has a sleek, simple look to it – it’s slim, compact, and the lightest of all of the flasks I tried, making it ideal for taking it with you on the go.
There’s a little button that releases the lid, so opening the flask is a breeze, and the mouthpiece is one of the best (if not the best) I've tried – wide and curved, for effortless, comfortable sipping.
When it came to the temperature test, my water was still chilled after a full 24 hours, as promised. Meanwhile, coffees and teas were still piping hot after 10 hours, so rest assured, this flask will keep drinks toasty until the commute home.
Buy now £17.56, Amazon.co.uk
Lifeventure TiV vacuum flask
Best: Budget flask
Material: 18/10 stainless steel, BPA-free
Weight: 445g
Capacity: 700ml
Max temperature preservation times: Hot for more than eight hours, cold for 24 hours
Dishwasher safe: No
Why we love it
- Slim and very portable
- Brilliant temperature retention
Take note
- The cup is fairly small
This 700ml flask boasts all the perks of a larger option while stripping away the extra bulk. With a copper coating to improve heat preservation, it boasts the ability to keep drinks hot for up to eight hours. Impressively, I found mine was still nice and warm after around 20 hours, which is pretty good going. Equally impressive was the flask’s ability to keep drinks chilled – there were still ice cubes in my cold water after 24 hours.
Should you prefer sipping hot tea and coffee from a cup rather than straight from the flask, this is a brilliant, compact choice. Unscrew the flask’s lid and it becomes a cup, although, admittedly, quite a small one, so you will probably need to fill it a few times to quench your thirst.
The flask isn’t dishwasher safe, but this is a minor annoyance with an otherwise very efficient and purse-friendly piece of kit.
Buy now £19.99, Lifeventure.com
Thermos stainless steel king flask
Best: Flask with a cup
Material: 18/8 food grade stainless steel
Weight: 650g
Capacity: 1,200ml
Max temperature preservation times: Hot for 24 hours, cold for 24 hours
Dishwasher safe: Yes
Why we love it
- Twist and pour stopper
- Collapsible handle
- Cup included
Take note
- The cup can get hot in your hands
As Thermos has become synonymous with insulated flasks, naturally, the supersize “steel king” was going to be pretty hard to beat. It has a whopping 1.2l capacity, and I was genuinely quite stunned by how hot it kept my water over 24 hours. Most of the ice in my cold drink was still solid after 24 hours, too – you could fill your Thermos in the morning and it will still be refreshingly cool the following day.
It’s sturdy but surprisingly lightweight for its size, and the handle, which is collapsible (to save on space), helps with one-handed carrying and pouring. Everything about the steel king feels exceptionally well-made – from the thick-rimmed stainless steel cup (which doesn’t have a handle but is still nicely capacious) to the twist and pour stopper. My one quibble would be that the stainless steel cup can feel hot in your hands when the liquid inside is especially scorching. However, never having to completely remove the screw cap before pouring will make for smoother al fresco pit stops. A classic for a reason, I can’t knock it.
Buy now £19.11, Amazon.co.uk
Klean Kanteen insulated TKPro
Best: Plastic-free flask
Material: Stainless steel and silicone and 18/8 food-grade stainless steel interior, BPA-free
Weight: 620g
Capacity: 750ml
Max temperature preservation times: Hot for 28 hours, cold for 90 hours when iced
Dishwasher safe: No, hand wash recommended
Why we love it
- Plastic-free
- Brilliant temperature retention
- Large cup included
Take note
- Bulky
Sleek and, thanks to being made with stainless steel, plastic-free, this flask from Klean Kanteen is an efficient and eco-conscious choice. Despite its fairly bulky design, at 750ml it’s not quite as capacious as some of the other flasks I’ve tested. However, it’s still going to be an excellent choice for bringing on longer outdoor adventures.
It performed ludicrously well when it came to preserving drink temperatures – my hot water was piping hot after 28 hours. I was extremely dubious about claims that it could keep iced water iced for 90 hours, and was flabbergasted to find it does exactly that (yes, really, almost four days).
Leakproof and cleverly designed, the flask features a twist and pour cap which can be poured from any angle – while slightly splashy if you don’t open it enough (or indeed too much), this is a really nifty way to save time and prevent some of the heat from escaping. I loved how capacious the stainless steel lid was too (216ml) and appreciated the wide mouth for comfortable sipping. It’s perfect when you’re gasping for a big cup of tea.
Buy now £42.95, Kleankanteen.co.uk
Ocean Bottle flask
Best: Environmentally conscientious flask
Material: 90 per cent recycled stainless steel, BPA-free plastic, silicone rubber and ocean-bound plastic
Weight: 320g
Capacity: 500ml
Max temperature preservation times: Hot for six hours, cold for six hours
Dishwasher safe: Yes
Why we love it
- Conscientious choice
- Versatile mouthpiece
- Carry loop for portability
Take note
- The mouthpiece can drip momentarily after the lid is removed
A conscientious choice when it comes to the materials used and environmental impact, this insulated flask from Ocean Bottle is largely made up of recycled stainless steel and ocean-bound plastic. On top of this, the brand says buying one bottle will fund efforts to prevent the equivalent of 1,000 plastic bottles from ending up in the ocean as plastic waste – so you can feel genuinely good about buying this one.
Water, coffee and even thicker smoothies and soups aren’t off limits, thanks to the bottle-esque mouthpiece. Easy to grab, owing to the flexible carry loop, you can unscrew the larger lid for cleaning and chucking in ice. My drinks were still impressively hot after six hours and refreshingly chilled after the same amount of time – cold enough that some of the ice I dropped in there was still intact. However, after using this bottle a fair bit, I’ve noticed that water collects between the lid and the mouthpiece so that when I unscrew the lid, it drips quite a bit. I thought this could be because I’d put it through the dishwasher when I shouldn’t have, but I checked, and the brand does actually state it’s dishwasher safe. This might be a one-off issue with the bottle I tested, or an issue through wear and tear, but it’s worth keeping in mind.
Buy now £35.00, Oceanbottle.co
Stanley adventure to go bottle
Best: Sturdy flask
Material: 8/8 stainless steel, BPA-free
Weight: 512g
Capacity: 750ml
Max temperature preservation times: Hot for 20 hours, cold for 25 hours (four days when iced)
Dishwasher safe: Unspecified
Why we love it
- Robust design
- Matte finish
Take note
- Splashy if you don’t unscrew the stopper enough
While this is a strapping flask from Stanley, it looks more streamlined and contemporary than the drinkware veteran’s classic designs. It’s a good size, but doesn’t feel overly bulky, and it promises to keep drinks hot for up to 20 hours, and cold for 24. Happily, these claims stood up during testing.
The lid doubles as an insulated cup, and, while it’s modestly sized, I think it’s big enough. There’s no chance of spills, as you might expect from a screw-in stopper, while little gaps in the stopper mean you can pour without having to unscrew it all the way. It’s a sturdy flask that gets the job done.
Buy now £41.00, Stanley1913.com
Contigo luxe autoseal travel mug
Best: Flask for easy, one-handed sipping
Material: 18/8 stainless steel, BPA-free
Weight: 320g
Capacity: 470ml
Max temperature preservation times: Hot for five hours, cold for 12 hours
Dishwasher safe: Yes
Why we love it
- The mouthpiece is convenient
- It’s small and compact
There’s something satisfyingly simple about this travel mug from Contigo. Press the large button on the lid, and your beverage will flow from a hole in the lid. As the flow of liquid is more concentrated than it is from larger mouthpieces, it feels almost similar to a mini vortex, which is fun. My water was hot after five hours, and cold after 12.
Drinking from this flask is a one-handed operation, as you don’t need to unscrew the lid before taking a sip. The lock on the lid will also prevent the button from being pressed when you don’t want it to be – say, when it’s being pushed up against your laptop in your bag. The flask is also very compact, narrow (making it easy to hold in one hand) and lightweight to carry. It’s a sleek bit of kit when it comes to design as well, with its all-over metallic finish, although there’s a range of other colours to choose from, too.
Buy now £29.95, Amazon.co.uk
Chillys series 2 lichen
Best: Flask for keeping water cold
Material: Powder-coated stainless steel, BPA-free
Weight: 390g
Capacity: 500ml
Max temperature preservation times: Hot for 12 hours, cold for 24 hours
Dishwasher safe: No, hand wash recommended
Why we love it
- Colour and design variety
- Antimicrobial drinking collar
Take note
- Unscrewing the lid can unscrew the drinking collar, causing leaks
Chilly’s has become somewhat synonymous with stylish drinkware – from dreamy ombre to abstract and floral bottles, there are plenty of styles to choose from. While you can use the brand’s insulated bottles for holding hot drinks (mine did a good job of keeping water piping hot for 24 hours), I would say I preferred using mine for keeping drinks cold. Some of the ice in my cold water was still intact after 24 hours and, naturally, the water was refreshingly chilled.
The series two bottles boast an antimicrobial drinking collar, which is dreamy to drink from and can be removed easily when it comes to cleaning the bottle, or dropping in ice cubes. This can sometimes open with the lid when it hasn’t been screwed on tightly enough, though, but the lid itself is completely leak-proof. Plus, the handle on the lid wins major points in terms of portability, while the protective rubber base means you don’t need to worry about making an obnoxious clang when setting down the flask.
Buy now £32.00, Chillys.com
Larq bottle purevis
Best: High-tech flask
Material: Stainless steel, BPA-free
Weight: 280g
Capacity: 500ml
Max temperature preservation times: Hot for 12 hours, cold for 24 hours
Dishwasher safe: Bottle is but the cap needs to be hand-washed
Why we love it
- Self-cleaning technology
- Stylish design
Take note
- Pricey
- Not recommended for tea and coffee
If you feel uneasy about water quality while travelling, Larq’s self-cleaning water bottle is a high-tech investment that has blazed a trail with its patented UV-C light hidden in the lid, eliminating nearly all (99.9 per cent) of bio-contaminants inside.
Looking a little sci-fi, the flask has a button on the lid, which can be pressed for either a short (one-minute) UV-C cycle, or you can choose adventure mode (three minutes) for extra peace of mind. Beneath the intimidating tech, though, the purevis is also just an excellent flask – my water remained hot after 12 hours, and there were still cubes of ice in my cold water after 24 hours. Importantly, please note that purification will be less effective with ice in the bottle, as this may partially block the UV-C light.
A clean bottle should help to keep that musty bottle smell at bay, and, while I admit I may have been swayed by the knowledge my water was completely clean, I did find my water tasted fresher for being purified. I liked that the bottle will clean itself automatically every two hours and, unlike the rest of my tech, only needs to be charged every month or so. It is worth noting that the brand doesn’t recommend using the bottle for drinks such as coffee and tea.
Buy now £89.00, Livelarq.com
Partner in Wine wine bottle
Best: Flask for wine
Material: Stainless steel and plastic lid, BPA-free
Weight: Unspecified
Capacity: 750ml
Max temperature preservation times: Hot for 12 hours, cold for 24 hours
Dishwasher safe: No
Why we love it
- Lightweight
- Good choice of colourways
Take note
- The mouth of the lid is too narrow fo ice cubes
As photogenic as they come, this insulated flask from Partner In Wine has been purpose-built for keeping your bottle of plonk cool for up to 24 hours. A great purchase if you really resent sipping on ever-so-slightly warm wine during the summer months, this would be perfect for filling up before picnics, festivals and any al-fresco gatherings when you would rather leave the wine cooler at home. It will fit one bottle of wine perfectly, and feels markedly lightweight for a bottle of this size (750ml).
While I wasn’t able to test this flask during the summer months, I still found that fridge-chilled wine stayed suitably cold for 24 hours. There’s no chance of vino spillages, either, as I can attest that the lid, which screws on easily and securely, is leak-proof. If you like ice in your wine, it’s worth noting the mouth of the bottle is quite narrow (indeed, wine-bottle narrow), so typical ice cubes won’t fit through.
While the black colour I tested is currently sold out, there are plenty of other dreamy hues to choose from, including soft pastels and all-over stainless steel.
Buy now £40.00, Partnerinwine.co.uk
Yeti 18oz bottle with hotshot cap
Best: Mid-sized flask
Material: 18/8 stainless steel, BPA-free
Weight: 531g
Capacity: 532ml
Max temperature preservation times: Hot for 24 hours, cold for 24 hours
Dishwasher safe: Yes
Why we love it
- The hotshot cap allows you to drink at any angle
Take note
- It’s not clear when the hotshot cap is closed
This flask is robust enough for outdoorsy excursions, but not so bulky that you wouldn’t reach for it for everyday use, so it’s a good choice for taking to work, too. While Yeti doesn’t specify a maximum heat retention time, I found that my water was still hot after 24 hours, while some of the ice in my cold water managed to survive for just as long.
Everything from the matte surface to the range of fun colours on offer suggests high-quality materials. I am also a big fan of the aptly named hotshot cap, which, once swivelled to one side, will let you sip from any angle. However, something to remind me whether or not the swivel mechanism had been ‘closed’ would have been really helpful.
What I consider to be the perfect amount of liquid flows through at the perfect speed (although this will be quite subjective) and the hotshot cap didn’t let me down when it came to being completely leak-free.
Buy now £29.95, Nordicoutdoor.co.uk
Hydro Flask coffee mug
Best: Insulated mug
Material: 18/8 Pro-Grade Stainless Steel, BPA free
Weight: 317g
Capacity: 355ml
Max temperature preservation times: Up to four hours
Dishwasher safe: No
Why we love it
- Versatile lid and mouthpiece
Take note
- Not leak-proof
Sometimes, it just feels better to drink from an actual mug than a flask – particularly when you’re not actually heading into the wild, but sitting at your desk, wanting your tea or coffee to stay hot for a few hours longer.
This insulated mug isn’t leak-proof, so you won’t be carrying it around in your bag, but if you tend to forget about your cups of tea until they’ve turned tepid, it’s ideal. The matte finish is nice in the hand, and while the brand doesn’t specify for how long it should keep drinks hot or cold, my boiled water was still fairly hot after four hours, which is all you really need for a tumbler like this.
When it came to ease of use, the lid can be placed on at any angle, and the mouthpiece slides open and close easily. The mouthpiece can also be removed completely, if you’d prefer to drink straight from the mug.
Buy now £24.96, Amazon.co.uk
Ohelo tumbler
Best: Flask with a strainer
Material: 18/8 stainless steel, lead- and BPA-free
Weight: 245g
Capacity: 400ml
Max temperature preservation times: Hot for six hours, cold for 12 hours
Dishwasher safe: Yes
Why we love it
- Strainer works well
- Variety of colourways
Take note
- No indication of when the lid is closed
- Taking it apart for cleaning is a little fiddly
A perk of Ohelo’s tumbler is the strainer, which I found worked well with my loose-leaf tea, but keep in mind you can’t easily remove the tea leaves on the go. Still, you could also use it for fruit infusions or lumpy protein shakes. To drink, you just need to twist the lid until it clicks into place, letting you know it’s open. The lid proved to be leak-free, and it’s quite helpful that you can take sips from anywhere around the lid, rather than just one mouthpiece.
The lid needs to be taken apart to be cleaned, and putting it back together is a little fiddly, but I got the hang of it. As for heat retention abilities, this little tumbler performs brilliantly – hot water was still impressively hot after six hours, and chilled after 12.
Buy now £29.00, Ohelobottle.com
Stanley quencher H2.0 flowstate tumbler
Best: Flask for style
Material: 90 per cent recycled 18/8 stainless steel, BPA-free
Weight: 635g
Capacity: 1.2l
Max temperature preservation times: Hot for seven hours, cold for 11 hours
Dishwasher safe: Yes
Why we love it
- Ergonomic handle
- Fits into some car cup-holders
Take note
- Not leak-proof
- It’s heavy
An unlikely product to have taken TikTok by storm, Stanley’s quencher flowstate can barely stay in stock. But is it worth the (considerable) splurge? Boasting a 1.2l capacity, the reusable tumbler keeps cold drinks chilled for up to 11 hours (or two days when iced). I tested these claims with an ice-cold smoothie, which stayed deliciously chilled. The ergonomic handle adds to its ease of use, while the narrow base that fits some (but not all) car cup-holders is a nice touch.
Though it’s easy to switch between the three lid positions, the full-cover top failed to pass the leak-proof test. This completely rules out the quencher in terms of carrying it loose in a bag, which is quite a big drawback, considering the price. There’s also no denying it’s heavy, and the sheer size of the thing is slightly impractical for lugging around a city during the commute. But when working from home, I appreciated the large capacity, as it helped boost my water intake (the colours are pretty, too).
Buy now £45.00, Stanley1913.co.uk
Thermos ultimate insulation flask
Best: Flask for commuting
Material: Stainless steel with silicone rings
Weight: 300kg
Capacity: 500ml
Max temperature preservation times: Hot for 24 hours, cold for 24 hours
Dishwasher safe: Unspecified
Why we love it
- Sturdy design
- Lightweight
This is a really solid little Thermos that does pretty much everything you’d ask of a flask. Thermos claims the flask retains temperatures for 24 hours, and it certainly did keep water cold and coffee warm over the full period. I was particularly impressed by how secure the flask felt, and I had no concerns about it leaking while bouncing around in my work bag on the Tube, in the car, or even while cycling, so it’s ideal for commuting.
The silicone rings make the flask feel extra sturdy, which I appreciated when out hiking, but, for most outdoor adventures, I’d probably opt for a flask that has a greater volume. That being said, it’s lightweight and has a decent 500ml capacity, which feels just right for taking tea or coffee into the office.
Buy now £24.99, Amazon.co.uk
Your flask questions answered
What’s the best flask?
Sleek, compact, and brilliant for sipping on the go, the Thermos superlight drinks flask was the top performer – I can’t recommend it enough for everyday use. I found that my water was still piping hot after 10 hours, and it doesn’t hurt that it also just looks great.
Lifeventure’s TiV vacuum flask offers excellent value for money as a budget-friendly option, while Klean Kanteen flask is ludicrously good at keeping drinks hot and cold for many, many hours.
The Ocean Bottle deserves a mention for being so versatile when it comes to carrying cold water, hot drinks, as well as thicker liquids like smoothies and soups, and I love that the brand is built on the premise of protecting the ocean by reducing plastic waste.
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