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Hydro Flask 18oz Standard Mouth



With a lifetime warranty and exceptional performance, it's an excellent albeit weighty and pricey choice for hot/cold drinks

At every product is thoroughly tested for as long as it takes to get a proper insight into how well it works. Our reviewers are experienced cyclists that we trust to be objective. While we strive to ensure that opinions expressed are backed up by facts, reviews are by their nature an informed opinion, not a definitive verdict. We don't intentionally try to break anything (except locks) but we do try to look for weak points in any design. The overall score is not just an average of the other scores: it reflects both a product's function and value – with value determined by how a product compares with items of similar spec, quality, and price.

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The Hydro Flask 18oz Standard Mouth Insulated Bottle plus Sport Cap is a rock-solid choice for keeping liquids hot or cold on a bike. Or in a kayak. Or a bag. Or just about anywhere life leads you. It's not light, and at £35 RRP (£25.95 bottle, £8.95 Sport Cap) it's certainly not cheap. But it does what it says on the tin, and has a lifetime warranty.

  • Pros: It keeps cold things icy-cold and hot things piping hot for many, many hours
  • Cons: Price, and weight, and limited to friction-fit bottle cages

Hydro Flask hails from Bend, Orgeon, and has been plying its insulated-container trade since 2009. It offers a range of cups, bottles and flasks for liquids and foods, in 14-and-counting colours, so it's likely you'll find one to match the overshoes or helmet.

> Find your nearest dealer here

Its secret sauce is the 'TempShield' technology, which according to Hydro Flask means it can 'guarantee no condensation or heat transfer to the outside of the bottle, ever'. To be clear, the Hydro Flask is an actual vacuum-flask – where there's no air inside between the inner and outer walls. This is different to pretty much every other 'insulated' bike bottle, where the heat transfer is slowed by a material.

We've tested a fair few insulated bottles on over the years (okay, seven), typically at the more premium end of the price range as you'd expect for products with more material and engineering involved. At £35, the Hydro Flask setup is nearly twice the price of the most expensive previously reviewed alternative – the Camelbak Podium Ice Bottle, which did an okay job of keeping things warm a few hours later.

Weighty matters

At 303g when fitted with the Sport Cap, which allows one-handed pull-with-your-teeth drinking (you can buy it online here), it's also heavy – over twice the weight of the Camelbak Podium Ice and three times the weight of most normal bottles. However, as you'll read below, the weight needs to be considered against the potential performance benefits in the round.

Hydro Flask - Standard Mouth Insulated Sport Cap.jpg

Shape-wise it's a smooth cylinder, which means it will be a bodged fit in a standard bottle cage where there's a retainer that snugs into the indented lip of a normal bottle. Increasingly, both bottles and cages are smooth, relying on overall friction instead of the indentation to hold the bottle in place. I trollied about the Highlands using the Hydro Flask in a non-indented Zefal Pulse Alloy cage, held snugly without rattle or the slightest hint of premature ejection. This was likely helped by the grippy powder coated finish, which is showing a few signs of use but nothing major.

The 18oz in the name means 18oz of water, or 532ml. Which is exactly what it takes. It being winter up here, I typically go for a weak herbal tea-and-honey mixture, the slight tantalising tingle of a few carbs usually more than enough to get me up the next bealach.

Drinking from a hard flask with a sipper top means there's wizardry at play, in the form of a one-way air ingress valve that lets the liquid flow freely without glugging or needing to suck so hard your lungs implode the alloy chamber within. I did feel that some air was mixed with the fluid, but not much.

When closed, the cap is certainly watertight – no amount of vigorous inverted shaking could generate even the slightest of leaks.

Running hot and cold

The raison d'être of the Hydro Flask is to keep warm things warm and cold things cold. This it does, in spades. During my tests over a few months of Scottish winter, I found it worked as well as any other high-end vacuum flask we own, for hiking, car trips and so on. And far, far better than any of the five or so 'thermal' bike bottles I've owned and tried in the last decade.

Most are good for a few hours, by which time a nice warm coffee or tea is a tepid disappointment. Not so the Hydro Flask – if you brewed it borderline burn-your-mouth hot before departing, you better be careful two or three hours later because almost nothing will have changed.

> Find more reviews of sports bottles here

Hydro Flask's warranty test is as follows: 'You can test the insulation property of your flask at home by adding boiling hot water to the flask. After 5 minutes, feel the outside of the flask (below the neck). If you feel any hot spots, the vacuum has been compromised and you are eligible for a replacement.'

There's a similarly-robust lifetime warranty on the cap leaking: basically, no questions, you get a new one.

Ice ice baby

Keeping things cold, Hydro Flask promises no condensation, and ice still present many hours later. This I was able to test up to indoors temperatures, and yes – ice cubes were still present in pre-chilled water 12 hours later, with the Hydro Flask sat in a 21-degree environment. And I don't mean 'a little bit of ice', I mean 'big chunks that look pretty much the same as when they went in'.

The science bit

Although the cycling hydration industrial complex wants you to believe you need many litres of fluid onhand for any ride longer than 5 minutes, for most people up to two hours of hard, unhydrated exercise is possible with no degradation in performance. Beyond that, however, you need a drink. Particularly in hot weather, the temperature of what you drink is as important as the volume consumed.

This 2016 University of Montana study found that when asked to do three hours of exercise in 31°C heat, drinking half the quantity of ice-slurry water showed "there were no differences in rectal temperature, heart rate, physiological strain index, skin temperature, sweat loss, or rating of perceived exertion" compared with consuming the full amount of ambient temperature water.

In other words, carrying a single bottle of iced water (835g for 532ml in the Hydro Flask) would deliver the same hydration benefit as carrying two bottles of the same volume ambient water, weighing in at around 1,400g total including cages. So riding for three hours on a hot day with an ice-slurry mix, you'll get the same benefit while carrying 565g less on the bike.

Or, as the study also found, carrying two bottles of the ice slurry and dosing yourself at the full rate will 'significantly improve' the above biometric criteria.

Yes, £35 is a lot of cash and yes, 303g is 'heavy', both comparable to the thermal-bottle competition. However, the hot-cold performance is in a league of its own for a cycling bottle, and the lifetime warranty is unbeatable. The fact the Hydro Flask comes with a non-sports cap for use with soups and suchlike off the bike adds to the utility, making the Hydro Flask a strong contender for your cash if you're after a lifetime of hot or cold nourishment, on or off the bike.


With a lifetime warranty and exceptional performance, it's an excellent albeit weighty and pricey choice for hot/cold drinks test report

Make and model: Hydro Flask 18oz Standard Mouth Bottle

Size tested: 18 oz = 532 mL

Tell us what the product is for

It's for people who need to keep about 530ml of liquid cold, cool, warm or hot, for many hours at a time, on or off a bike.

Hydro Flask says: "Keeping your fluid intake on the upside is easy when you've got this portable travel buddy. Whether you're headed to the gym or a quick jaunt across town, you can easily take your refreshment with you."

Tell us some more about the technical aspects of the product?

From Hydro Flask:

Product Benefits

Ideal for pairing with our Standard Mouth Insulated Sport Cap for one-handed refreshment

TempShieldTM insulation eliminates condensation and keeps beverages cold up to 24 hours or hot up to 12 hours

Durable 18/8 Pro-Grade Stainless Steel construction

BPA-Free and Phthalate-Free

Lifetime Warranty

Volume 532 mL

Mouth Diameter 1.91"

Diameter 2.87"

Height 8.7"

Weight 11.3 oz

Rate the product for quality of construction:

The feel and finish of the Hydro Flask is top notch.

Rate the product for performance:

The Scottish winter daylight hours aren't long enough to test this product from 'hot' to 'cool', it's that good at keeping things warm.

Rate the product for durability:

Made like a tank, and with a lifetime warranty.

Rate the product for weight (if applicable)

This is really the only gripe – at over 300g, it's a portly beastie.

Rate the product for comfort (if applicable)

Drinking form the Hydro Flask is comfortable.

Rate the product for value:

I have a drift of 'insulated' bottles in a drawer, which probably cost me over £50 all-up. All are moderately useless beyond two hours, therefore of little 'value'. The Hydro Flask beats all of them, for a small weight penalty. I think that makes it good value.

Tell us how the product performed overall when used for its designed purpose

Can't fault it.

Tell us what you particularly liked about the product

The insulated Sport Cap works really well.

Tell us what you particularly disliked about the product

Nothing, really.

Did you enjoy using the product? Yes

Would you consider buying the product? Yes

Would you recommend the product to a friend? Yes

Use this box to explain your overall score

There's no getting away from the price or weight, but for the experience this delivers it still warrants a four stars/very good rating.

Overall rating: 8/10

About the tester

Age: 44  Height: 183cm  Weight: 72kg

I usually ride: Merida Ride 5000 Disc  My best bike is:

I've been riding for: Over 20 years  I ride: A few times a week  I would class myself as: Expert

I regularly do the following types of riding: cyclo-cross, club rides, general fitness riding, mountain biking, Dutch bike pootling

Living in the Highlands, Mike is constantly finding innovative and usually cold/wet ways to accelerate the degradation of cycling kit. At his happiest in a warm workshop holding an anodised tool of high repute, Mike's been taking bikes apart and (mostly) putting them back together for forty years. With a day job in global IT (he's not completely sure what that means either) and having run a boutique cycle service business on the side for a decade, bikes are his escape into the practical and life-changing for his customers.

Add new comment


Richard D | 6 years ago

I have two stainless steel "Kleen Kanteen" bottles (one insulated, one not).  Sod the weight penalty, they look so good on a Ti-framed bike!

barbarus | 6 years ago
1 like

I think I have a non-standard mouth; will this still fit me?

On a more serious note, I use a monkii cage and lifeventure mug to solve this sort of problem but this looks better, with the dual lid option.

Tass Whitby replied to barbarus | 6 years ago
1 like

barbarus wrote:

I think I have a non-standard mouth; will this still fit me? On a more serious note, I use a monkii cage and lifeventure mug to solve this sort of problem but this looks better, with the dual lid option.

There's a wide mouth version, if you're more Mick Jagger than Donald Trump...

If you are tempted to buy one, just make sure it fits your cage - it doesn't work with some cos of the shape. 

ktache | 6 years ago

I love my Elite Deboyo flask, with coca cola details, I use the insulated non bicycle type lid, which means I do have to stop to drink but it stays warmer and good tea tastes better with a thin lip on the cup.

It's so good it quickly became my at work cup as I can make a good brew and it stays hot for a good hour with no lid.

On those truely gutting days when I have not placed it on the bike (will not fit in the rear bottle holder when in the workstand) the tea is still tepid when I get home over 12 hours later.

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