Hydro Flask 18oz Standard Mouth

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 road.cc 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.

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 road.cc 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.

Verdict

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