Warm up on cold days with a hot drink or soup. We've put flasks and thermal cups through their paces to find the best on the market. Read on to find out which products came out on top.
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When the temperature drops, a flask or thermal cup is a worthwhile investment, as you can keep a drink or soup hot while out and about. You'll also save money, as you'll avoid the need to buy coffee or soup in shops and reduce your use of disposable cups and single-use plastics. In the summer, flasks can also help keep drinks cold.
We put 22 popular products through their paces to find the ones you should consider. For more, visit our review section and find over 200 practical buyer's guides offering unbiased advice on what equipment is worth investing in.
Thermos stainless King flask, 1.2 litre
Best overall flask
Pros: feels light even at full capacity
Cons: could do with a second cup
Tea test score: 10/10
This stainless-steel flask is large and proudly bears the Thermos name, but most importantly, it works.
Despite plenty of competition, Thermos is still the most instantly recognisable name in the market, and it offers an extensive range of products to keep food and drink hot or cold.
We tested the 1.2-litre capacity flask in bold red, but there are plenty of colour options available. All aspects of its design have been carefully considered. For instance, the cup is insulated with plastic, so our tea retained its heat over a long period but the flask wasn't too hot to hold.
The flask features a simple screw-top cap that can be loosened for pouring, and ensures not too much heat escapes.
Although the flask is on the hefty side, a sturdy, loose-hinged metal handle makes it easy to use and carry. Its handsome metal cup easily screws on over the cap.
The flask is just over 30cm tall (including the cup) and weighs in at 1.8kg when full, despite being quite light when empty. We didn’t find any signs of leaks around the cap, and pouring was good with no excessive dripping.
Best of all was its performance. Its label promises the flask will keep drinks hot for 24 hours, and when we finally opened it a day after making our tea, it was as hot as when we’d brewed it the morning before.
This flask is reliable and immensely practical, and with a confident 50-year guarantee, it could remain a staple of family days out for years.
Eva Solo to go cup, 350ml
Most stylish cup
Pros: can be easily used with one hand
Cons: it won’t keep your drink hot all day, but great for a few hours
Tea test score: 6/10
Standing 20cm tall, this brushed stainless-steel thermal cup comes in a wide range of coloured tops (ours was green) to add to its sleek appearance. It looks elegant, but also impresses with its thought-out features.
First, we liked its clever lid mechanism. To sip your drink, simply flick a plastic disc to reveal the opening. Another flick will close it again. It’s so easy you can do it with one finger, which is great when you're on the move.
It's also slender enough for most adults to easily grip in one hand and operate the cap at the same time.
Finally, we thought the flexible silicone handle attached to the cap was immensely useful, while also in keeping with the cup’s cool design.
Beyond its good looks, it kept drinks warm enough – if not scalding hot – for six hours. There was no residual taste from previous drinks, and it was easy to clean and stood up to being dropped. This is an ideal flask for the commute or gym.
Rex flask and cup, 350ml
Best value flask for one person
Pros: small and convenient, suitable for any occasion
Cons: cup isn’t insulated
Tea test score: 6/10
There's certainly no lack of choice in the Rex range, with plenty of designs to choose from that appeal to both adults and kids.
We tested the apple-patterned flask and cup, which was stylish and cheerful as well as robust. With a capacity of 350ml – about the size of an average mug – we found this was an ideal flask for one person to use.
The single cup attached to its top holds roughly as much as a small tea cup, and has a tiny handle for extra support. Although the cup is basic and lacks insulation, we found it perfectly adequate.
The flask itself has a press-button top, meaning you press it in to pour your drink and then press it again to lock it. Not having to remove the full cap reduces the amount of heat that escapes when using it, so liquids stay hot for longer.
We found no signs of leaks, pouring was trouble-free and the flask was a doddle to wash-up by hand. The cup easily slotted back on top until needed again.
The leaflet that comes with the flask doesn’t make any specific claims about how long it keeps drinks hot. This could be frustrating if you're looking for one to use all day long, and may put some people off. We gave it an initial six-hour test and found our tea was still very drinkable after that time.
Small enough to pop into a coat pocket or handbag, we thought this was ideal for keeping drinks warm for one.
Klean Kanteen TKWide, 355ml
Most innovative cup for one person
Pros: simple to use and just as easy to clean
Cons: its exterior paint could chip if handled roughly
Tea test score: 9/10
During testing, we came across a variety of different types of caps for both thermal cups and flasks, but this one stood out for being easy to use and secure.
The cap on the TKWide boasts an opening and closing mechanism that you can operate with one finger if needed. An effortless quarter turn of the cap locks it, while moving it back a quarter opens it, allowing you to drink or pour out the contents.
You can also remove the cap completely to drink from its wide opening. A no-hassle thread means screwing the cap on is simple.
Another excellent design feature is a discreet flip-down metal handle that fits snugly into the cap when not in use. Thanks to its slightly roughened coating, the cup is also easy to grip.
We gave this flask big ticks for keeping drinks tasting fresh, with no lingering tastes or odours from previous use. It was also easy to clean and had no leakage issues.
But however clever the design, a flask is only a winner if it keeps a drink hot, and this got top marks on that front. It claimed it would work for 11 hours, and our drink was still hot when we checked after this time.
Our overall impression of it was being solid and reliable and – with that nifty cap feature – a clear winner.
Klean Kanteen (£25.95)
Tefal travel mug, 360ml
Best thermal cup
Pros: easy to open and close, and safe in the dishwasher
Cons: no obvious flaws with it
Tea test score: 7/10
This easy-to-grip travel mug with a slightly raised, soft-feel outer surface is a sound investment if you're looking to keep drinks warm for yourself.
It has a sleek appearance and comes loaded with practical features. We liked the push button on the lid – push it in to drink from it, push it again to lock it and seal in heat. There's no need to remove the lid to drink, which is great for use on the go.
As a plus, it's safe for use in the dishwasher so it can be thoroughly cleaned.
At 360ml, it holds a decent-sized mugful and promises to keep drinks hot for four hours or cold for eight. After four hours, our drink was still a perfect temperature, and even after our six-hour test it was still fairly hot.
The mug isn’t the cheapest, but a five-year guarantee should mean it’s built to last, be it on the commute or otherwise on the go.
Most reliable midsized flask
Pros: drinks came out as hot as they went in
Cons: no handle for carrying it
Tea test score: 10/10
This Swedish-designed double-walled flask promotes itself as crucial kit for the rugged adventurer, so you might feel it’s a bit much for your Sunday afternoon stroll in the countryside, but you can be assured that it won't let you down, no matter the activity.
It feels sturdy, and at 26cm is quite tall, but doesn't feel bulky – its sleek shape means it can easily be slipped into a backpack without much fuss.
We found it easy to grip, and its slightly textured surface means it won't slip if your hands are wet or you’re wearing gloves.
It comes with two stoppers, regular and click-close – the standard feels hefty and helps retain heat while the click-close stopper allows you to drink straight from the bottle. Both have grooves to help with grip. You can also use the stainless-steel cup that screws on over the stopper.
We were impressed by its ability to keep liquids hot: it promised eight hours, but even after 12 hours, our tea was still warm.
Easy to wash and with no fiddly accessories, this is a go-to flask for any occasion.
Best flask for the family
Pros: great size, good looks, easy to clean
Cons: doesn’t come with a cup
Tea test score: 9/10
This large, chunky bottle holds nearly 1 litre, so it's great if you're looking to carry enough for a small group or family. The shape is broad rather than tall (it’s 23cm high), making it easier to fit into smaller bags. It's functional and looks simple, but possesses plenty of charm.
The flask is surprisingly light and the handle on the lid makes it very easy to carry. The handle also feels very secure, and is soft so it doesn't dig into your hand, which is a bonus.
It comes in array of colours, and our dusky lilac oversion was stylish without being too overt in appearance.
There’s no cup so you’ll need to bring mugs for everyone, but the exceptionally wide mouth makes pouring very quick and easy. You could also take turns drinking from the bottle.
An added advantage of the wide mouth is that it's easy to clean. It’s made of high-grade steel, so it is able to withstand any falls or knocks.
This flask claims to keep drinks hot for 12 hours or cold for 24, which it did well. We found little to fault and much to praise.
Hydro Flask (£37.95)
Orla Kiely oval flower orange vacuum flask, 750ml
Most stylish flask
Pros: great looking slim flask
Cons: could easily scratch if handle roughly
Tea test score: 9/10
This is an eye-catching flask that is functional as well as stylish. It has a retro 70s vibe, but still manages to look sleek and modern with a slender shape and bright colours. The orange cup matches the overall design nicely.
The cup itself is triple-insulated, so it had no trouble keeping our drinks warm after pouring. It was comfortable to hold thanks to a small handle, though the cup was on the small side itself. The flask opens and closes with a push button on the lid, keeping contents toasty for longer. We found no problems when pressing this repeatedly while testing.
The flask comes with a promise to keep drinks hot for up to 12 hours, and our tea was still perfectly warm and drinkable after this time.
Annabel James (£29.95)
Most practical small flask
Pros: small, streamlined design
Cons: no handle
Tea test score: 7/10
Everything about this stainless-steel flask is really neat and cosy-looking. It comes in a cute tweed wrap finished with a leather-look trim, which is removable. The wrap does protect the steel finish from scratches – a useful feature.
The flask is slim, compact and unflashy. It is 25cm tall, and fits nicely in a day bag or large waterproof pocket. There’s no handle, but it’s easy to grip and stays cool to the touch.
To access your drink, remove the lid (which doubles as a cup) and twist the top to partially open it and pour. The little cup doesn’t have a handle either, but as it’s insulated it wasn’t too hot to hold.
There was no indication on the packaging as to how long the flask would keep drinks hot, so we tried it for six hours and the coffee was still warm enough to drink, if not scalding.
Best value family flask
Pros: great value, great size
Cons: will be too bulky for some
Tea test score: 9/10
This is a big, no-nonsense flask and its sizeable capacity is perfect for those times you want to take tea or coffee for a small group on an outing. The solid flask has a lightweight plastic lid that doubles as an extra cup, as well as a large main cup that is bigger than nearly all of the others we tested.
The soft, rubber-feel handle is flexible, and lays smartly along the side of the flask. The handle of the cup lines up with it too, giving it a streamlined look.
You can pour your drink by opening it up, or by flicking a small red switch on the stopper to pour without opening.
Our tea was really hot after the six hours it claimed. It didn't scratch or dent during testing and was fairly robust. As it's such good value, any family that likes to get out and about would find this an essential piece of kit.
Which flask should I buy?
Flasks come in a huge range of shapes, sizes and openings, and with varying claims as to how long they'll keep drinks hot or cold. Here are some factors to consider when choosing a flask.
We tested flasks that could hold enough for several people (or someone wanting several cups during the day) as well as some that were designed to serve one. The size you need should be based on your individual needs, as well as the activities you might be doing while using it.
A large-capacity flask that’s completely full can be a hefty addition to your bag, so you may want to look for a streamlined, lighter flask to start.
For how long will it keep drinks hot?
If you’re buying a flask for the commute, a short 'keep hot' time will be fine, but if you’re a hiker planning day-long treks, you’ll want one with a longer promise. Our samples made pledges ranging from four to 24 hours, so there’s plenty to choose from.
Mug or flask?
Some flasks are effectively insulated travel mugs, so if you’re looking for one for just yourself, that may be fine. The difference is usually that you drink out of them directly rather than pouring the drink into the cup.
How will you carry your flask? If you want to slip in into a pocket or take it in backpack, you'll want to pay attention to the shape. Would you prefer one that’s tall and thin, or will that end up poking out of the top of your pocket? Will one that is shorter but wider take up too much space in your bag? Consider your options carefully before investing in one.
On some flasks, you need to unscrew the top before pouring, while others open by pushing a button (or similar). This keeps the contents hotter for longer as you’re not exposing them to cold air. If you’re after a single cup of tea, that won’t be an issue, but it’s something worth considering if you’re planning to enjoy your drink over a few hours. If you’ll be juggling a number of things, like children and shopping, you might prefer a flask with a simpler, one-button mechanism or similar.
As a general rule, flasks can’t go in the dishwasher, and some slender models might be tricky to wash without a bottle brush. Wider openings are generally easier to clean.
Our sample ranged from £10 to £80.
Is there a guarantee with your flask, and if so, how long does it last? A couple of our samples came with lifetime guarantees, which was very impressive.
What we looked for in a flask
Effectiveness We tested the flasks on two different ‘effectiveness’ criteria. First, did it stand up to its stated claim – for example, if it said it would keep water hot for 12 hours, did it achieve that? We also filled the flasks or cups with boiled water and then used that water to make a cup of tea for our 'tea test', and scored it out of ten based on how hot the resulting drink was.
Value for money Was the flask worth its price tag?
Style A flask can be practical and stylish. We looked at the design from an aesthetic point of view.
Design and functionality We looked for important design features that can make a real difference, such as insulated cups, easy-open tops and strong handles.
Innovation We awarded our flasks extra points if they had any particularly clever features.
Leaks A flask that leaks is at best annoying and at worst dangerous. We tested all the flasks for leaks, and we’re pleased to report that none of them did.
This review was last updated in October 2019. If you have any questions or suggestions for future reviews, or spot anything that has changed in price or availability, please get in touch at firstname.lastname@example.org.