When you’re on watch, few things will revive you like a piping hot cup of tea of coffee. Having it to hand in a vacuum flask, tucked away in a cockpit cubby and ready to refresh you at the twist of a lid, is a comfort in itself, and on a rough passage it avoids the unpleasant necessity of having to venture into the boat’s stomach-churning bowels. And how else might you enjoy a brew while antifouling in the off-season?

As these are insulated flasks, they’ll keep things cold too, so you can stop the milk going sour, or fire up the tender and find a deserted
beach with a flagon of ice-cold Chablis in your backpack. But which flask will keep your coffee warmest or your wine coolest?

Most claim to keep liquids hot or cold for 24 hours or more, though it doesn’t specify what ‘hot’ or ‘cold’ actually means. Does it mean ‘hot’ when it went in, or is there an EU standard for ‘hot’? Regardless, we needed to do this test because two things guaranteed to disquiet the spirit are tepid tea and warm white wine. So, we collected eight one-litre vacuum flasks currently on the market to find out whether one was better than the other – and whether you really get value for money if you spend a little more.

9 of the best vacuum flasks tested

Tempa Ultimo

Specifications

HANDLE: Yes
CUPS: Two
FLOATS FULL: Not tested
FLOATS WITH NO CUP: Not tested
HEIGHT: 34cm

This is a chunky beast, but it’s also light, has a handle and comes with two decent-sized cups. The cap is a screw gate so you can unscrew it a couple of times for pouring tea, or all the way to fill.

The base unscrews so you can take the inner flask out and put it in the dishwasher. It’s the only dishwasher-safe model here, but take care, as the flask itself is glass.

The 24-hour temperature drop – second lowest on test – was disappointing, because we thought glass might insulate better. We broke the glass flask when removing it for inspection, so it may be too fragile for the inevitable hard knocks sustained at sea.

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Vango

Specifications

HANDLE: No
CUPS: One
FLOATS FULL: Yes
FLOATS WITH NO CUP: Yes
HEIGHT: 29.5cm

This is as simple as a flask can be, and made in stainless steel so it’s not going to break. There’s no handle, which means it’s going to roll around a bit when it falls over – again, no problem for the stainless steel interior although you’ll need to put it down carefully if you want it to stay put.

It also comes with a single, quite small, plastic-lined cup, which screws onto the top. It’s another screw gate cap, so pouring tea involves nothing more than a couple of turns of the cap, but you can also remove the top completely for soup. It came bottom in our 24-hour heat retention test, losing 45 per cent of the liquid’s heat.

Highlander FLA105 Tufflask

Specifications

HANDLE: Yes, strap too
CUPS: One
FLOATS FULL: Yes
FLOATS WITH NO CUP: Yes
HEIGHT: 28cm

Here’s another stainless steel flask but, unlike the Vango, it has a plastic fold-flat carry handle – which also stops it rolling around too much – and, uniquely in this test, it comes with a strap.

There’s just the one cup, so you’ll have to share it, but it’s a biggie, plastic-lined, and it screws onto the top securely. The cap is a push-button model, push the centre to open it and the outer to close.

You can unscrew it, too, to get your soup out and to fill it. Performance-wise, it faired about as well as the Tempa Ultimo, losing 44 per cent of its heat over the 24-hour period, which isn’t great.

Mountain Warehouse

Specifications

HANDLE: No
CUPS: One
FLOATS FULL: Yes
FLOATS WITH NO CUP: Yes
HEIGHT: 31.5cm

This is an aluminium model, lighter but not significantly so, with a faintly rubberised finish, making it easier to grip. It has no handle so it will need to be tough to survive the inevitable tumbles its tall, tower-like structure invites.

The single plastic-lined cup isn’t a particularly generous size and has no handle. The cap is a pushbutton model, press the centre to pour and the outer to close. It also unscrews completely for filling or for decanting your minestrone.

In terms of performance, it was a step-up from most of the others, losing 39 per cent of its heat 24 hours after the test began, but still not a sparkling effort from this camping all-rounder.

Buy it now from Mountain Warehouse

Lifeventure TiV

Specifications

HANDLE: No
CUPS: One
FLOATS FULL: Yes
FLOATS WITH NO CUP: No
HEIGHT: 32cm

Here’s another stainless steel flask coated with a rough finish to improve grip. Being vaguely projectile-shaped, it will fall over and roll around, so you’ll need to be careful where you leave it but at least it won’t break when, inevitably, it does bounce off the cockpit sole.

There’s one plastic-lined cup, again on the small side so you’ll have to hand it around, and uniquely in this company, it comes with a choice of stoppers, pushbutton or pouring. If it drops in the drink without its cup screwed on, it will sink, but it’s worth recovering because it performs quite well. After 24 hours, this model had lost exactly a third of its heat.

Buy it now from Lifeventure

Thermos Hercules

Specifications

HANDLE: Yes
CUPS: One
FLOATS FULL: Yes
FLOATS WITH NO CUP: Yes
HEIGHT: 33.5cm

From the biggest name in the business, this muscular-looking flask goes by the name of Hercules, and it looks every bit as strong.

Its plastic shell has roll-stops on the side and a handle, which is very helpful on a boat, and the flask inner comprises a vacuum between two stainless steel shells, so it’s going to survive the inevitable knocks.

The single plastic-lined cup is one of the biggest on test and the cap is a screw gate that removes for filling. It floats like a fender and retained heat better than any other flask on test, losing just 23 per cent over the 24-hour period. It’s a impressive beast and our test winner.

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Aladdin Challenger

Specifications

HANDLE: Yes
CUPS: Two
FLOATS FULL: Yes
FLOATS WITH NO CUP: Yes
HEIGHT: 32cm

This is another sturdy looking vacuum flask fashioned from stainless steel and featuring a big plastic handle. There are two cups, the top is plastic-lined stainless steel and slightly smaller than the lower plastic one.

The cap is a screw gate that twists for pouring and unscrews completely, too. It also has stowage in the base, useful for sugar if you’re sharing with someone who takes it.

In terms of performance it was the second best on test, losing just 29 per cent of its heat in 24 hours. This performance and the twin cups almost secured ‘best on test’ status but in the end the Thermos Hercules edged it on performance and value, as it costs a third less.

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Stanley Classic

Specifications

HANDLE: Yes
CUPS: One
FLOATS FULL: Yes
FLOATS WITH NO CUP: Yes
HEIGHT: 35.5cm

This flask from American thermal stalwarts Stanley, aptly-named The Classic, comes complete with memories of tartan rugs, grazed knees, hayfever and jam-and-wasp sandwiches.

Hewn from stainless steel with a Hammerite-style outer and a plastic handle to stop it rolling around excessively, it’s hefty and designed to handle the knocks. It also comes with a 25-year guarantee.

There’s a single plastic-lined cup screwed on top and the cap is a screw gate style that also removes completely. Its performance was also slightly nostalgic, losing 31 per cent of its heat over the 24-hour test period. It’s undoubtedly tough and we loved the retro look, but the Stanley Classic struggles a bit with performance and value.

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How we tested the best vacuum flasks

Pre-warming with boiling water, or pre-cooling with iced water, for five minutes is recommended practice for any flask. After pre-warming, we filled each one with hot water from the same source, measured its temperature as 86.5°C, then checked the temperature 24 hours later to see which flask had best retained the heat.

Although you’re unlikely to wait 24 hours before you have your tea, we wanted to exaggerate performance in search of a clear winner.

We also checked to see which would float when full (with and without cups), just in case your flask should escape overboard. We then noted which had handles, straps, lanyards and other useful features.

Conclusion

As stated, you wouldn’t wait 24 hours before unleashing the steaming contents of your flask, unless it’s been a particularly savage watch, but we wanted to find a clear winner so our test was taken to the extreme. Many of the flasks on test claim to keep liquids hot or cold for 24 hours, so we investigated what that means.

The Thermos Hercules was the clear-cut winner in the finish. It has only a single cup but most boats have a few spare mugs stowed on board so it’s not a catastrophic omission, but in every other respect it was the best on test.

Only one was dishwasher friendly, the Tempo Ultima, but the best way to clean a flask is to rinse it out with clean water. Woe betide those who swill theirs out with soapy water or a treatment of bicarbonate of soda.

Didn’t find what you’re looking for? Head to Amazon’s dedicated sailing page for more marine products.