Whether you’re traveling into the backcountry or internationally, clean water isn’t always a guarantee. Yes, you can buy bottled water if you’re in a different country, but what’s even better is carrying a bottle that can filter water from nearly any fresh water source in the world.

There are a few bottles with integrated filters on the market, including the LifeStraw Peak Series Bottle, which we reviewed in the past. But when we heard that HydraPak — a brand famous for high-performance, outdoor-centric water storage products — was making a collapsible bottle with a built-in filter, we knew we had to try it.

We got our hands on the new HydraPak Flux+ 1.5L to give it a try, and after weeks of testing, there are a few things we don’t like but still a lot to love about this bottle.

It isn’t perfect, but this collapsible bottle has an incredible flow rate and a durable exterior, making it a top dog in the market of bottles with built-in filters. Difficulty keeping it clean, particularly in the long term, hold it back from being a truly great option.

Collapsible water bottles with integrated filters seem to be a growing trend in the outdoors industry, and we couldn’t be happier about it. Carrying a completely separate filtering system can be cumbersome in the backcountry, and these all-in-one water bottles are not only great for drinking clean water in nature but also while traveling.

The HydraPak Flux+ 1.5L has all the benefits you’d expect from a bottle in this category. Its collapsibility is stellar, its filter allows you to drink water from nearly any water source and it’s designed to be as small and light as possible.

This is HydraPak’s first foray into filtering, but you don’t have to worry: The filtering technology is up to par. According to HydraPak, the filter is a single stage, smaller than .2 micron hollow fiber filter that can remove 99.9999% of common waterborne bacteria, 99.999% of parasitic cysts per EPA Guide Standards and NSF P231 and 99.999% of microplastics per NSF 42 greater than or equal to 3.0 microns in size. That’s the same percentages as LifeStraw Peak Series Collapsible Water Bottle’s filter for parasitic cysts and microplastics; however, the LifeStraw can remove more bacteria at 99.999999%.

To test the filter, we filled the bottle with a bunch of soil and filtered the water into a clean cup. Not a spec of dirt made it through the filter; however, it still had quite a bit of dirt taste to it (similar to the LifeStraw). The biggest surprise, though, was just how good the flow rate of the HydraPak Flux+ is. We’ve used other water filters before, including the LifeStraw Peak Series bottle and the Sawyer Squeeze, but the HydraPak easily has the fastest flow rate of any filter we’ve tested. That means drinking out of the bottle is much easier, and it actually feels like drinking from a normal bottle.

The bottle’s flow rate wasn’t only fast, but it was consistent too. During our filtering tests, most filters immediately slow down as the soil clogs up the filter. That wasn’t the case with the HydraPak. Even after filtering multiple bottles of extremely dirty water, it kept its super-high flowrate.

On top of its speed and efficacy, we absolutely loved how small the HydraPak Flux+ can get. It scrunches down onto itself to about the size of a softball, and can get even flatter if you remove the filter. The bottle has a loop on the top that not only acts as a way to clip your bottle onto your backpack but can also fold over the scrunched-up bottle to keep it compact. Although, when the filter is inside the bottle, it’s really hard to get the loop around the entire bottle. For that reason, we wish the loop were just a little bit bigger or had some stretch to it.

The bottle can pack down super small, which helps it fit into any bag, but when it’s full, the HydraPak Flux+ has an impressive 1.5-liter capacity. In testing, we really enjoyed this size, as it’s bigger than your standard water bottle but doesn’t feel massive.

Another great aspect of the HydraPak is its material and overall shape. It’s got a completely flat bottom, which means when the bottle is full (but only when it’s full), it can actually stand up by itself. The material also feels a lot thicker than that of the LifeStraw bottle we tested, which ended up getting a tiny hole after a few months. We’ll keep using the HydraPak bottle and squeezing water through it to keep this post updated with any durability issues.

There’s a lot to love about the HydraPak Flux+, but there are a few things we didn’t like. The biggest issue in our opinion is the fact that you can’t backwash the filter. Most other filters come with some sort of syringe so you can push clean water back through a clogged filter, which cleans it and helps it retain its peak flow rate. The HydraPak Flux+’s 42mm filter doesn’t have this option.

To clean it, HydraPak recommends dipping the filter in clean water and shaking it around to loosen up and remove any debris. After our filtration tests we did this, but after more than 10 rounds of shaking the filter, bits of soil were still coming out. This is an annoying and time-consuming process in the short term, but since there isn’t a way to quickly and effectively get all the debris out, the long-term flow rate of the filter doesn’t seem promising. HydraPak states the filter should be replaced after a year or after 1,500 liters of water have been filtered, depending on the quality of water. In comparison, LifeStraw says its filter’s life span is 2,000 liters.

The filter itself is tough to clean, and the bottle itself isn’t a walk in the park either. Unfortunately, you can’t throw it in the dishwasher, but with a bottle brush you can scrub the insides pretty easily.

One last thing we wanted to point out was that the cap of the HydraPak Flux+ can be quite hard to open. You’re supposed to flip it open, then twist, but the lip on the cap is small and it took a lot of effort to pop it open, especially when it was brand new.

The HydraPak Flux+ is quite similar to the LifeStraw Peak Series Collapsible bottle, but we do like HydraPak’s option a bit more. The filter might not last as long since you can’t backwash it, but we think the LifeStraw’s lack of durability really sets it back. Katadyn also has a collapsible water bottle, which we haven’t tested yet, but it’s famous for its stellar flow rate.

If you don’t want to deal with the shortcomings of the all-in-one bottles, you can mix and match your filter and reservoir to find your perfect pair. There’s a wide variety of options, including HydraPak’s new 28mm filter — the size that fits standard plastic water bottles — which is a direct competitor to others that have long been popular in the backpacking community like the Sawyer Squeeze. There are other filters that come in the 42mm size like the Katadyn BeFree, and you can even use HydraPak’s Plug-N-Play adapter to attach a 42mm reservoir to a 28mm filter. However, we still haven’t found the Goldilocks bottle that packs everything into one neat package so you can skip all the research.

HydraPak’s Flux+ 1.5L water bottle has a great flow rate and is built with thick, durable materials. We wish its filter were easier to clean and keep up, but overall it’s a great option in the collapsible bottle scene. If you don’t want to parse through different reservoirs and filters and want one do-it-all bottle, and you don’t mind replacing the filter cap every once in a while, the HydraPak Flux+ is a great pick.