I took this Hydro Flask on a freezing hike to test its 'hot for 12 hours' promise

The Hydro Flask Lightweight Trail Series Bottle claims to offer a similar experience to the rest of Hydro Flask’s insulated water bottle range, but with one surprising omission: weight. It’s a simple pitch – a quality insulated bottle in a range of sizes, but 25% lighter than existing models – but one that makes a lot of sense. Even today's best Thermos flasks can be on the weighty side. 

With the Trail Series, ice cold water (or juice, etc) can be kept cold in the summer heat for 24 hours, according to Hydro Flask, and hot drinks can be kept warm for 12, or so the marketing rhetoric goes. If it actually works, this could well be one of the best hiking water bottles around. So I decided to put it to the test and see if it actually works.

I set out on a day’s walk with a 32oz HydroFlask (the largest in the range) to see how long we’d have hot tea to enjoy, having primed it with boiling water and a mint tea bag. Ambient temperatures were low-to mid single figures (I'm talking degrees Centigrade here), so relatively mild in winter terms, with little wind to add a confusing wind-chill factor into the experiment, and the HydroFlask as exposed as possible to the elements, tucked into an outside water bottle pocket in the rucksack. 

I also brought a pocket-sized thermometer along for the ride to keep tabs on just how quickly the HydroFlask loses heat. Of course, the old-school winter walker tip here is to fill your flask with hot squash, which is equally tasty whether drunk hot or cold, unlike, say, tea. But will such grey-beard trickery be required with the HydroFlask? 

After a couple of hours we stopped for a snack and a drink. Checking the flask, it’s immediately obvious that the contents are still hot – the lid is noticeably warm, while the metal bottle itself is cool to the touch, thanks to the double-wall insulation. Steam rises, and the tea is still too hot to drink immediately, good news for later tea-drinking attempts. 

A couple of hours later we checked again, four hours after filling the flask. The tea is still hot – now just about drinkable, but only carefully, in sips. It’s still over 70 degrees in the HydroFlask, raising our hopes that we will indeed make the 12 hour mark and still be warm. Or certainly warmer than the 4C it is outside now. A thin drizzle is inevitably falling, making the tea all the more welcome. 

Mid-afternoon now (3pm), and the tea is cooling down, but very slowly. It’s now 65C, which is comfortable to drink, but still hot. The outer flask is downright cold to the touch, demonstrating just how good that insulation is, as well as making it quite a surprise to get hot tea out of it! With the shorter winter days, dusk is rapidly approaching, so in a final push we turn back towards home. 

Hours later, at 5.30pm, we check the flask again just before leaving the car park. It’s still at 55C, a pleasantly warming – and hydrating – end to the walk. There’s still a fair amount of liquid left, so we check it again at 10.30pm that evening, a full 13 hours after filling. The tea is now 45 degrees, so still drinkable in a pinch, but needless to say somewhat past it’s best. That said, it’s also a solid 43C degrees above ambient temperature, and would be a welcome warmer if we were still out in the cold. 

Overall, it’s hard not to be impressed with the Hydro Flask Lightweight Trail Series Bottle. It kept boiling water hot for well over the promised 12 hours, albeit getting a bit cool in the last hour or so, but that’s no mean feat. Although there is a bit of a weight penalty – 356 grams for the largest size as tested here – there’s the robust build quality to factor in. The latter is not only good news for longevity, but also the rest of your pack contents, which won’t appreciate a leak from a cheaper, less well built flask. Another major plus in very cold winter conditions is that this won’t freeze up like standard water bottles often do, making it an ideal all-seasons water bottle, especially considering the easy-fill wide-mouth.