The HydraPak Flux (2.7 oz / 77 g, MSRP $20 for the 1L version) is a soft-sided, collapsible, 42 mm threaded, reusable water-bottle aimed at the single-use Smartwater or sports-drink bottle crowd.

HydraPak Flux 1L review: Stock Photo
The HydraPak Flux 1 L. Photo: HydraPak

The Problem

When I first took up the sport of long-distance backpacking in a serious way, my first instinct was to use Platypus-style soft-sided bottles. I appreciated their compressibility and weight, and I liked that they were not single-use. At the time, I was proud of myself for not using a big, heavy Nalgene bottle (we all start somewhere, right?).

But soon enough, the realities of trail life took their toll on my good intentions. I found this style of bottle challenging to fill from shallow pools or lakes when running water wasn’t available. They don’t dry out easily, don’t stand up well, and their softness and floppiness can make them hard to get in and out of pack pockets while on the go. On top of all that, they can’t take much abuse—at least they didn’t as of a few years ago (the last time I seriously put a Platypus bottle through its paces).

And so I did what a lot of thru-hikers do: I gravitated towards single-use plastic bottles, namely 1 L Smartwater bottles. As most of us know, Smartwater bottles hold up well (I usually use them for a month or so at a time) and have a long, skinny shape that slots nicely into most pack pockets. Some packs are even designing pockets with Smartwater bottles in mind, which I find to be a fascinating development. 750 ml (25.3 oz) sports-drink bottles are also popular for many of the same reasons.

But since becoming a full-time outdoor journalist, I find myself increasingly facing the realities of our community’s impact on the environment. I’m starting to do some thinking about my carbon impact with regards to traveling to a trail-head. I’m self-conscious about all the single-use plastic baggies in my food-packing strategy. And finally—and this is a big one—I’ve finally decided that it’s time to give up my beloved Smartwater bottles.

Enter HydraPak

The HydraPak Flux 1 L is the newest product from HydraPak, a company that’s taken a noticeably different approach to soft-sided bottles than Platypus and similar competitors. Readers may be familiar with the Stash – HydraPak’s original 1 L bottle. The Stash has a screw-off lid, a bail handle, weighs 3.7 oz (107 g), and is made with durable TPU and PP materials.

This design is notable because although it’s soft-sided, it stands up on its own when empty. This function comes with several benefits – notably that filling from difficult water sources is easier, and your drinking nozzle doesn’t get dirty from laying on the ground. Thanks to the material selection, these bottles are far more durable than either Platypus soft-sided bottles or single-use plastic bottles.

The 1 L Stash has a 63 mm threaded lid, and so it is nice if you want a wide opening and/or use a filtration device that matches that thread size (most of the pump-style ones do). But until recently, you had to go down to the 750 ml (25.3 oz) size to get a 42 ml (read Katadyn BeFree compatible) lid.

I prefer 1 L bottles, and the 3.7 oz (105 g) weight was just a little too much for me to pull the trigger on. And like most ultra-lighters, I don’t use pump-style filters.

The Flux Pros

And now we get to the Hydrapak Flux. This product retains all the great things about the Stash and tweaks the design to appeal to a broader range of ultralight needs.

HydraPak Flux 1L review: Flux Water Bottle
The HydraPak Flux 1L retains the useful features of the HydraPak Stash but incorporates them into a lighter product.

The Flux retains the bail handle, my favorite feature for keeping my hands out of cold water and filling from ponds with ease. The Flux also keeps the strong yet flexible construction, welded seams, and compressibility; although it doesn’t compress quite as neatly as the Stash. And of course, you get HydraPak’s signature feature–that standing-up-when-empty ability.

HydraPak Flux 1L review: Flux Water Bottle
The bail handle is one of my favorite features of the HydraPak Flux 1 L. I hate getting my hands into cold water first thing in the morning.

The Flux’s first difference is that you get a 42 mm thread with 1 L of storage, meaning that 1 L bottle fans can pair it with a Katadyn BeFree no problem.

The lid is still screw-off (for easy lemonade/chia seed/electrolyte additions) but now has a squeeze nozzle.

HydraPak Flux 1L review: Flux Water Bottle Open
The 42 mm thread is compatible with Katadyn BeFree filters—a major plus.

The final point, of course, is the weight. The 1 L Flux weighs 2.7 oz (77 g). That’s still 1.3 oz (36 g) heavier than a Smartwater bottle, but 1 oz (28 g) lighter than the Stash. For some reason, that one ounce was just enough of a mental nudge for me to make the switch.

HydraPak Flux 1L review: Milliliter marks on the Flux Water Bottle
Indicator marks for milliliters are another little benefit over using a single-use plastic bottle.

The Hydrapak Flux Bottle: Cons

There’s a lot to like about the Hydrapak Flux Bottle, but it isn’t all roses and sunshine. My load-hauling Rogue Panda Zoro has water bottle pockets designed with long, skinny, hard-sided Smartwater bottles in mind, and my Flux bottles are nearly impossible to get in there (go check out the pack to see what I mean).

HydraPak Flux 1L review: The water bottle has a larger base than a Smartwater Bottle
Trying to get the HydraPak Flux 1 L into the specially designed (for Smartwater bottles) pocket of my Rogue Panda Zoro. It didn’t go so well.

I had slightly better luck when pairing Hydrapak Flux bottles with my Mountainsmith Zerk 40 L Fastpack. That pack utilizes a much more traditional side-pocket system. So, if that’s how your pack is designed, you might be better off. But it still wasn’t as easy as when using a Smartwater bottle. So I’ve come to accept this drawback as a necessary evil of switching away from single-use bottles. I’d rather re-think my bottle storage system entirely (and possibly commission a backpack with soft-sided bottles in mind) than continue to use single-use plastics.

HydraPak Flux 1L review: More difficulty with water bottle retrieval
Having a little more luck getting the bottle in and out of traditional side-pockets, but it still isn’t great – and I should note that the Zerk 40 L pictured here is one of the easier packs I’ve ever used for water-bottle retrieval.

A final thought: It’d be nice if the Hydrapak Flux could handle boiling water for use as a hot-water bottle in extreme conditions, but it maxes out at 140 F (60 C). You could maybe get away with attempting to heat up water to just below that point, but that seems foolish, dangerous, and easy to get wrong.


I can tell you that HydraPak has a hard-sized reusable bottle coming out this October. This bottle is Smartwater-shaped and made of 50% post-consumer plastic. Called the Hydrapak Recon, it might be a good middle-ground between Nalgene bottles and Smartwater bottles. I’ll post a blog about it later this fall once I’ve had a chance to test one out.

What’s your current water-bottle setup? Are you thinking about ditching single-use plastics for more reusable (but heavier) options? Drop me a line in the comments and let me know where your head is!

Disclosure: some of the links above may be affiliate links, which means if you place an order at one of these retailers, we receive a small commission on this sale. This helps support Backpacking Light, thank you!

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