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Best Thermos Flasks 2026 | Tested and Reviewed |
In addition to this initial temperature test, all of these flasks have also been thoroughly tested across UK landscapes at various times of the year. This ensured that the flasks could perform well with both hot and cold liquids, and could hold up to the demands of life on the trail.
Related: Best Gifts for Hikers
With a primary focus on hiking, walking, and backpacking; we also tested these flasks on kayaking trips, on travels abroad, on bikepacking adventures, and on everyday dog walks. These were key tests in determining factors such as durability and ease of use, as well as the almighty test of time.
The Best Vacuum Flasks Of 2026 – Our Results
Including top options from leading brands, as well as lesser-known brands with equally impressive offerings, here’s our favourite thermos flasks for 2026.
- Thermos Ultimate Series Flask 500ml – Best Flask Overall in Our Tests
- Quechua 0.8L Insulated Steel Flask 900 – Best Value Insulated Flask
- Hydroflask Hot Flask and Cup 36oz (1.06L) – Best Large Insulated Flask
- Mizu D7 23oz Bottle – Best Plastic-Free Thermos Flask
- Stanley Classic Legendary Bottle 0.75L – Most Durable Thermos Flask
- VSSL Rift 20oz Tumbler
- Klean Kanteen TKPro 1L
- Primus Trailbreak EX 1 Litre
- Camelbak MultiBev Bottle 650ml with 480ml Cup
- Lifeventure TiV 700 Vacuum Flask
- Hydro Flask Lightweight Trail Series 24oz Wide Mouth
- Yeti Rambler 16oz
- Outwell Wilbur Vacuum Flask
- S’well Traveler 16oz Bottle
Editor’s Note: This article was updated in January 2026 to ensure that all of the products are still available for purchase. Further recent updates include the addition of Hydroflask’s Hot Flask and Cup which earned the title of ‘Best Large Insulated Flask’ after impressing one of our tester’s this winter. Stay tuned for updates as we continue our testing throughout the winter season.
1. Thermos Ultimate Series 500ml – BEST BUY
The best thermo flask overall, according to our tests.
Thermos Ultimate Series 500ml
★★★★★
Price: £33.50
Weight: 295g
Best for: Hiking, hillwalking and general outdoor use
Pros: Class-leading performance, durable, relatively lightweight, integrated cup
Cons: None so far!
The Thermos Ultimate flask is our original winner and, judging from the results of our most recent temperature tests, it’s still the best. This stainless steel flask is very durable, with a silicone base to protect against dents. The two-part stopper closes securely yet pours easily and has an integrated cup.
In terms of outright heat-holding performance for up to 8 hours, nothing can touch the Ultimate Series. It was the best-performing flask we tested overall. It is relatively lightweight too. And if you’re concerned that the 500ml capacity will be too small, it’s worth noting that Thermos also makes a larger 900ml version.
Full Specifications
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.
2. Quechua 0.8L insulated steel flask 900
This was our choice as best value insulated flask overall.
Quechua 900 0.8L
★★★★
Price: £15
Weight: 366g
Best for: General outdoor and everyday use
Pros: Easy to open/close, good temperature retention, very durable, useful handing loop
Cons: Narrow opening, a little wide at the base, harder to clean than most
This was a solid performer in the temperature tests and also happens to be one of the lowest cost flasks in our tests. As such we’ve deemed this to be worthy of our pick as best value insulated flask overall.
It’s smart looking, very durable, and the flip top makes it very easy and convenient. We found we were able to drink from it one-handed, and the textured base made it usable while wearing gloves too.
We did find that there were some drawbacks, however. First of all, it’s narrow opening and multi-part lid did make it harder to clean than some of the other flasks in our tests. It’s also quite wide at the base so it’s not cup holder friendly or the easiest to slide into the side of a backpack – though it does have that useful hanging loop.
Full Specifications
Capacity: 800ml (27oz) / Temperature test: 0 hrs 90°c, 90 mins 88.9°c, 4 hrs 78.6°c, 6 hrs 71.8°c, 8 hrs °66.1c, 24 hrs 41.3°c / Stainless teel double wall vacuum with a layer of copper / Dishwasher safe.
3. Hydroflask Hot Flask and Cup 36oz (1.06L)
The best large insulated flask in our tests.
Hydroflask Hot Flask and Cup
★★★★½
Price: £31.95 (sale)
Weight: 720g
Best for: Long day hikes, road trips, camping holidays, long climbing days
Pros: Excellent performance, hard-wearing, sleek and narrow build, lifetime guarantee
Cons: Pricey, too bulky/ heavy for lightweight hiking or backpacking
The Hot Flask and Cup is Hydroflask’s answer to the kind of traditional, burly thermos flask you might have seen your Grandad take on a fishing trip. Updated, of course, with modern technologies that ensure your liquids stay hot/cold for up to 30 hours, it’s similar in concept to Stanley’s Legendary Bottle, but with Hydroflask’s distinctive styling and a narrower build.
OM tester Jazz has been using the Hot Flask and Cup all throughout winter, most recently on some hikes throughout Fermanagh and Donegal in Ireland. She said: “This has been the ideal companion for big days out this winter. Most recently, I’ve used it for surfing days in Donegal, day hiking in the Cuilcagh Lakelands geopark, and on a few canoeing excursions across Lough Erne. I’ve actually also used it at home a lot, when I want copious amounts of peppermint tea but am feeling too lazy to boil the kettle each time (a bit ridiculous, I know).”
“For me, the heat-holding performance has been excellent every time. I also like the narrow build – it means it can fit in the side of most hiking backpacks without any issues which is surprising considering how much it holds. While it’s too heavy/ bulky for backpacking trips or lightweight hiking days, I think it excels on big outdoor days or group road trips when you know you’ll be needing loads of brews to keep the gang going.”
“The pour-through cap is a particular highlight for me as it makes decanting your drink so much easier and more spill-proof, especially when you’re out and about in in windy/ precarious pouring conditions.”
Full Specifications
Up to 30 hours hot or cold / TempShield double-wall vacuum insulation / Leakproof when closed / Integrated cup securely attaches to bottle / Pour-through cap / Comfortable carrying handle / Durable 18/8 pro-grade stainless steel / Not for use in a microwave or freezer / Lifetime guarantee / Available in 28oz (800ml) and 36oz (1.06l) capacities.
4. Mizu D7 Stainless Steel Insulated Bottle
Best plastic-free thermos flask.
Mizu D7
★★★★
Price: £47
Weight: 515g
Best for: Hiking, hillwalking and general outdoor use
Pros: Durable, stylish, integrated cup, plastic-free construction, leakproof
Cons: Didn’t perform as good as other flasks in our temperature tests
This 22oz (680ml) vacuum insulated bottle from Japanese brand Mizu combines classic looks with some more utilitarian, outdoorsy touches – namely that paracord carry handle and stylish powder-coat finish. It features a copper lining and a vacuum sealed cap, and the design is completely plastic-free.
The slimmer size slips easily into a pack and will also fit in most car cup-holders. On test, it proved completely leak-proof, and we particularly liked the screw-on double wall cup, which is a practical size for sipping coffee or soup. It doesn’t get hot enough to burn your fingers or lips either. It was a mid-range performer in our temperature test, placing 7th out of 14 flasks overall. The contents were still hot (well over 60°c) after 8 hours.
Read our full Mizu flask review.
Full Specifications
Capacity: 22 fl oz (680ml) / Temperature test: 0 hrs 90°c, 90 mins 84°c, 4 hrs 76.8°c, 6 hrs 71.4°c, 8 hrs 66.9°c, 24 hrs 45.4°c / Stainless steel interior and exterior / Cool-touch, no-slip finish / Integrated cup / Cord carry handle.
5. Stanley Classic Legendary Bottle 0.75L
This gets our pick as the most durable thermos flask. It’s hard to beat a Stanley.
Stanley Classic Legendary Bottle 0.75L
★★★★
Price: £52 (member’s price: £44)
Weight: 595g
Best for: General outdoor use
Pros: Excellent performance, robust and durable, integrated cup
Cons: Heavy and bulky
This heavy-duty flask has an effective easy-pour stopper that reduces the chance of spillages. The integrated cup is a good size and has an insulated rim to prevent burnt lips. You can actually get more in the flask than the manufacturer’s stated capacity too – we filled it up to 800ml. It’s a well-made and durable flask with very good heat retention. In fact, this was one of the best performers in our temperature test.
The only possible drawback is that the chunky design adds weight and bulk to your pack. Still, it’s the kind of product that feels like it’ll last for years of use, and it’s versatile enough for everything from day hikes to winter camping. With its classic design and reliable performance, it’s easy to see why Stanley bottles have built such a strong reputation.
Read our full Stanley flask review.
Full Specifications
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.
Best of the Rest
6. VSSL Rift Tumbler 20oz
VSSL Rift Tumbler 20oz
★★★★
Price: £39.95
Weight: TBC
Best for: Everyday use, road trips, travel, hiking
Pros: Tough materials with recycled content, slick look, useful features, comfortable to grip
Cons: Not the highest performer on this list
VSSL, in case you didn’t know, are a Canadian brand best known for their rugged coffee making gear. We recently got our hands on their Rift tumbler and have liked what we’ve seen so far. In particular, we admired the fact that it’s made from recycled stainless steel, something only a few drinkware brands are doing at the moment so kudos to VSSL for that.
OM editor Will has been using the 20oz Rift flask this spring, most recently on an adventure-focused trip to Croatia. He said: “To start with, I really like the look of the flask – it’s very slick looking, with a minimalist design that feels like it’s built to last. On test, the materials feel quite tough too, and it’s been genuinely comfortable to grip.” Another feature of the Rift that’s particularly useful is the twist-lock lid that seals the flask shut using a silicone gasket. We’ve had no spills or leaks so far, even on one cycling side quest where the flask got really thrashed about in the side pouch of a backpack.
“I also like the silicone base”, Will continues. “I’ve found it grippy on a variety of surfaces, and think it’s really handy when you’re on a lunch break mid-hike and don’t have loads of flat options to rest your flask on. Those are the scenarios when you need a flask you can rely on to not topple over and spill your long-awaited tea all over the grass. Thankfully, the Rift has been reliable in that respect.”
All in all, we think this is well-made and very versatile flask that will suit a range of different contexts, from day-to-day use and weekend road trips right through to big day hikes and multi-day adventures.
Full Specifications
20oz capacity: 591 ml / 20 oz dimensions: 23 x 9.3 x 9.3 cm / made using recycled 18/8 stainless steel / double wall vacuum insulation / lockable lid with latch / anti-slip silicone base / cup holder friendly / can sip one-handed / dishwasher safe / BPA-free / available in 10 & 16 oz capacities / lifetime guarantee.
7. Klean Kanteen TKPro 1L
Klean Kanteen TKPro 1L
★★★★
Price: £48
Weight: 723g
Best for: Camping and general outdoor use
Pros: Excellent performance, durable, lightweight, pours from any angle
Cons: Narrow mouth, hard to clean, pricey
This is an exceptionally durable and robust steel flask with no plastic components. The integrated cup is double-walled and has a generous capacity, while the stopper features a unique thread design that aims to minimise heat loss while also facilitating pouring from any angle.
Despite its chunky looks, this was the lightest of the 1-litre flasks we tested. It also retains heat impressively well and was the best performer after 24 hours. The mouth of the flask is relatively narrow, which probably helps to keep heat in, but makes filling and cleaning a little tricky. This was also the priciest flask we tested. Still, in our opinion, this is the flask to take on extended trips when you need to keep a brew hot for hours and hours and hours…
Full Specifications
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.
8. Primus Trailbreak EX 1 Litre
Primus Trailbreak EX 1 Litre
★★★★
Price: £38.66
Weight: 740g
Best for: Expedition use, winter adventures
Pros: Large capacity, very durable, comes with two stopper designs, easy to fill and clean
Cons: Heaviest on the list, could have performed better in our tests
This is a robust and durable bit of kit for even the most demanding conditions. It’s supplied with a non-slip silicone sleeve that improves insulating performance and makes the flask very resistant to scratches and dents.
You also get two stoppers as standard – one regular stopper for maximum temperature retention and one ClickClose-stopper that enables you to drink directly from the flask. In addition to its extremely rugged construction, the wide mouth makes filling and cleaning the flask easy, while the two different stoppers included with the flask make it very versatile too. We also liked the cup design. But it is one of the heaviest flasks here. We also expected it to perform better in our temperature test – it only placed 7th overall. We found it a bit difficult to screw the regular stopper in properly.
Read our full Primus Trailbreak Flask review.
Full Specifications
Capacity: 1 litre (33oz) / Temperature test: 0 hrs 90°c, 90 mins 85.5°c, 4 hrs 79.1°c, 6 hrs 74.3°c, 8 hrs 69.9°c, 24 hrs 44.5°c / Made of food grade 18/8 stainless steel that doesn’t impart or retain flavour / Lid doubles as a mug ensuring you always have a cup handy / Silicon sleeve / Drinking stopper opens and closes with a slight turn / Additional standard stopper for optimum heat retention included / Tapered design for easier handling / Large mouth opening is easy to fill and clean.
9. Camelbak MultiBev Vacuum Insulated Stainless Steel Bottle 650ml with 480ml Cup
Camelbak MultiBev Bottle and Cup
★★★★
Price: £22.50
Weight: 645g
Best for: Hiking, hillwalking and everyday use
Pros: Durable, BPA-free, easy to clean
Cons: Limited insulating abilities
Though perhaps best known for its hydration systems and water filters, Camelbak also makes a range of double-wall vacuum flasks. This includes the versatile MultiBev, which is a 2-in-1 vessel water bottle and tallboy-style coffee mug. This makes it a great daily companion, as you can use it for morning coffee and for water throughout the day. The mug unscrews from the bottom of the flask and there’s a handy roll-and-fold silicon lid hidden in the top cap.
It also has a non-slip silicone base and a practical carry handle. The flask is also easy to clean, dishwasher safe and BPA-free. It works better as a bottle for chilled water than a coffee flask though, as overall heat-holding performance was disappointing in comparison to rivals. In fairness the contents of the flask was still hot after six hours, measuring over 60°c. But beyond that, the insulation seems to reach its limits.
Read our full Camelbak Multibev review.
Full Specifications
Capacity: 650ml / Temperature test: 0 hrs 90°c, 90 mins 79.7°c, 4 hrs 69.7°c, 6 hrs 63.1°c, 8 hrs 57.5°c, 24 hrs 36.3°c / Includes ‘roll and fold’ silicone lid / Leak-proof cap with carry handle / Non-slip silicone base / Powder coat finish.