Nobody will be surprised when we proclaim that a flask is an essential piece of caravanning kit.

They mean drinks – hot or cold – are available in-car on all journeys, saving money at pricey service stations, plus they are great for days out.

So what should you consider when buying a flask?

How we tested them

First, we pre-warmed each flask to 95°C, then emptied the water out, raised it to 95°C again, and then refilled the flask again – all were then left for 12 hours to see how much the temperature inside dropped.

In real life use, caps play a big part in keeping a flask’s contents hot or cold.

Caps with built-in pour systems mean that although cooler ambient air replaces the fluid poured out, at no point can the hot air funnel out as it can when the cap is removed completely – and caps with pouring lids are a big bonus thermally, but some are better than others.

And if you intend to use a flask in tea/coffee pot mode, you ideally want a pour/stop control with a simple button or lever.

We also considered other ease-of-use factors, such as how easy they are to clean – and if the cap has a button-operated pouring mechanism with numerous internal components, can it be dismantled and re-assembled easily when cleaning?

Next, we see if you can drink straight from the flask. Some newer designs have travel mug-style caps – and how easy are they to drink from?

Another bonus is a wide-necked flask, as it’s also good for storing hot food in.

Finally, we check that the flask stays sealed, even when upside down.

Let’s see how these 14 stainless steel flasks perform!

Lifeventure 800 – four stars

  • Price: £18.99

This is the only true food flask in the line-up, sporting a wide enough neck to allow ladles and other implements to fit in.

Naturally, the wide neck also makes cleaning much easier – dishcloth use may even be possible if you have thin enough hands.

Reflecting its foodie nature, Lifeventure has included a small bowl, which sits within the cap.

But does a large flat cap mean compromised thermal performance? In short, no.

In the test this kept its contents slightly hotter than the winning Primus.

But the non-dismantling cap lost points as you have to leave it to soak clean.

Lifeventure TiV Vacuum Flask – four stars

  • Price: £20.99

Lifeventure’s second entry is a surprisingly good performer.

Unlike premium brands, such as Stanley, Thermos and Primus, no bold claims are made about how long this unit will keep its contents hot or cold.

So it was a surprise, in our thermal test, to find that this was just a whisker behind the top three.

But it seems that outstanding thermal performance comes at the cost of practicalities.

The neck is very narrow, ruling out food usage, other than thin soups. And cleaning out is only achieved by fill-and-shake or bottle brush.

The lid can be fully cleaned easily, but its pour speed is tediously slow.

Buy the Lifeventure TiV Vacuum Flask here from Amazon

Thermos Stainless King – four stars

  • Price: £24.95

It’s hard not to like this flask’s stunning retro styling.

And yet once you move on from there, the overriding impression shifts from looks to the fact that this is a huge amount of flask for the money.

And by that we’re not simply referring to its 1.2-litre capacity – the largest in the group.

With its stunning finish quality and outstanding thermal performance, it’s hard objectively to make a call between this and the two Stanleys here.

That is, until the price is considered. Ultimately this is 12 quid less than the cheaper of the Stanleys, despite pretty much matching it in terms of features and thermal ability.

All round, then, this is a real contender.

Buy the Thermos Stainless King here from Amazon

Primus Trailbreak EX – five stars

Practical Caravan Editor’s Choice

  • Price: £36

This is an innovative design from the respected Swedish flask maker.

Although not a true food flask, its neck is pretty wide – meaning thick soups are fair game, and it’s a doddle to clean.

Talking of hygiene, the cap dismantles easily, allowing full cleaning of its internal components, and, when assembled, it’s probably the best bit of the unit.

A smooth-moving, finger-operated twist ring opens and closes the pour hole, and the cleverly shaped top can be supped from just like a travel mug.

Thermally this isn’t the top performer here, but it’s still excellent.

We don’t doubt the 20 hours hot/cold rating claimed.

Buy the Primus Trailbreak EX here from Amazon

Lakeland Sip & Pour Flask – three stars

  • Price: £11.59

Here’s a product that truly blurs the lines between a traditional flask and a travel mug.

Just press a small button – which can be locked down to prevent accidental operation – and the top pings up to reveal exactly the same spout arrangement as most travel mugs have.

But make no mistake, this is a true flask. It’s actually a pretty good one.

All parts of the cap and spout arrangement are accessible for thorough cleaning. And even the inside of the flask itself can be got to easily, thanks to a surprisingly wide neck.

Sadly thermal performance trails almost all the others here, but it’s still better than most travel mugs.

Buy the Lakeland Sip & Pour Flask here from Lakeland

Robens Wilderness Vacuum Flask – three stars

  • Price: £12.99

Much like Lakleland’s Sip & Pour flask, this is essentially a hybrid between a conventional flask and a travel mug.

In fact, its neck is almost wide enough for the unit to be classed as a food flask, too. So far, then, so good.

But what’s the catch? Well, unfortunately, this was the worst thermal performer in the group.

This rules it out as something to take on long walks or for lengthy journeys in the car.

But you still have a keenly priced, large capacity, travel mug-cum-food flask, with superior thermal properties to most standalone mugs. And it doesn’t leak.

Buy the Robens Wilderness Vacuum Flask here from Amazon

Stanley Classic Vacuum Bottle – three stars

  • Price: £36.99

Thermos Stainless King’s retro appearance looks great, but this model’s equally yesteryear styling has something extra: authenticity.

In short, Stanley has been making this flask, in the same way and style, for decades. So does that mean the design was right from the start?

Oh, yes. As well as being incredibly durable – even to the point of still working if dented – this flask narrowly beat every other model here in the thermal tests.

In other ways, however, the design does feel dated.

The neck, for instance, is extremely narrow and deeply recessed, and that can make cleaning incredibly challenging.

Buy the Stanley Classic Vacuum Bottle here from Amazon

Stanley Master Series – three stars

  • Price: £44.69

Practically all flasks feature twin walls, with a vacuum between them, to keep the heat in or out.

Stanley’s new Master series is different in coming with Quad Wall insulation, which is essentially two sets of twin walls doubled up.

In theory, this should dramatically outperform every flask here thermally. Yet our test results simply don’t bear this out: this model was even marginally beaten by its older Stanley Classic sibling.

But the premium price isn’t just about enhanced thermal characteristics.

This top-of-the-range model not only comes with a lifetime warranty, but it is also dishwasher safe – unlike any other product here.

Buy the Stanley Master Series here from Amazon

Thermos Thermocafe – three stars

  • Price: £11.49

Granted, Thermos’ second entry doesn’t have the visual appeal of its first. But in most ways, the two flasks have the same pros and cons.

Once again, thermal performance is impressive. In fact, it was the sixth best here.

So while it wasn’t quite in the same league as the other Thermos or the two Stanleys, it was still good enough to beat our ultimate winner, Primus’ Trailbreak EX.

But, once again, out-and-out thermal ability seems to have been put ahead of usability.

The narrow neck rules out using the product for anything other than drinks. And cleaning is by bottle brush, or fill and shake, only.

Buy the Thermos Thermocafe here from Amazon

UKHS 946673 – three stars

  • Price: £11.95

If we had an award for the most capacity for the least money, this UKHS model would take it.

Put simply, here’s a one-litre flask for around the cost of most half-litre models.

And while you’d be forgiven, at this stage, for suspecting that you only get what you pay for, here’s another surprise: this is really rather good.

In the all-important thermal stakes, it is only the tiniest fraction behind the all-conquering Primus.

And we certainly didn’t expect the slick push button on/off pour switches at this price level.

Our only gripe is that the cap cannot be dismantled for really thorough cleaning.

Zanussi Cervinia Vacuum Flask – three stars

  • Price: £22.99

Not a name we usually associate with flasks, but that might change if this model is anything to go by.

We love the natty black and yellow design (the exact opposite colour scheme, yellow with a black capacity indicator, is also available) and the coating almost feels like rubber: this is certainly not a flask that will slip out of your hands easily.

But if you blot out the snazzy finish, this is a close relative of the UKHS flask. On the bright side, the cap has the same push button operation.

And thermally, the flask is right on the heels of the top three. But the cap can only be cleaned by soaking.

Buy the Zanussi Cervinia Vacuum Flask here from Argos

HydroFlask – two stars

  • Price: £35

This looks like a contemporary reimagining of the common flask and we’re not sure the results justify a price that rivals the Primus and Stanley.

The main problem is lacklustre heat retention. Thermal performance is better than the Robens and Lakeland travel mugs-cum-flasks, but only just.

The lack of a useful mug may freshen up the flask’s appearance, but it would work better if the cap had a travel mug-style spout. It hasn’t.

Worse still, you have to unscrew the cap fully to get to what’s inside, and the neck is too wide to drink from easily.

And while the neck is wide, it’s not wide enough for food like Lifeventure’s 800.

Buy the HydroFlask here from Amazon

Lakeland Corkcicle Canteen – two stars

  • Price: £21.99

As eyecatching as this American design is, the Corkcicle suffers the same issues as the HydroFlask.

It looks good, and it’s obviously a modern interpretation of the conventional flask, but what benefits do these design tweaks bring?

In truth, not a lot. Again, the lack of an on-board cup could be excused if the cap had a mug-style spout on it. It doesn’t.

Instead, the top has to be fully removed to drink anything, which is time consuming and not great from a heat retention point of view.

And because the top of the flask is made narrow enough to fit in the mouth, this is another one that’s not easy to clean.

Buy the Lakeland Corkcicle Canteen here from Lakeland

Outwell Aden – one star

  • Price: £10

Any flask can double up as a coffee or tea pot, to keep drinks hot at the table in cool UK weather. And in this role, the Aden isn’t a bad piece of kit.

It looks right, and the sprung pour lever is much faster to operate than unscrewing, or fully removing, a conventional flask’s cap.

But whereas other fast pouring flasks – such as the Primus, Zanussi, Lakeland, and UKHS models – also work well as conventional flasks, this doesn’t.

When shut, it leaks slightly. And even if it didn’t, there is nothing to stop the pour lever being pressed accidentally when the flask is being carried in a bag.

Buy the Outwell Aden here from Amazon