The world's most in-depth and scientific reviews of outdoor gear

LifeStraw Flex Review

While this product is very versatile, it's on-the-go performance lagged.
LifeStraw Flex
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Price:  $35 List | $34.84 at Amazon
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Pros:  Inexpensive, lightweight, versatile
Cons:  Leaky bottle, super slow flow rate, hard to suck through
Manufacturer:   Vestergaard
By Amber King ⋅ Senior Review Editor  ⋅  May 6, 2019
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65
OVERALL
SCORE


RANKED
#16 of 18
  • Water Quality - 20% 8
  • Durability & Maintenance - 20% 4
  • Treatment Time - 15% 8
  • Weight & Packability - 15% 8
  • Ease of Set-Up - 15% 8
  • Ease of Filtration - 15% 3

Our Verdict

We were intrigued by the Lifestraw Flex given its plethora of uses. Filtering out bacteria and protozoa (including Giardia and Cryptosporidium), this mini filter comes with a soft bottle and is relatively lightweight. At first glance, we were excited to think that there is a lightweight option that can do all this. However, when we tested it, we were a little disappointed.

In all of its forms, this filter is tough to suck water through. The tiny output makes the flow slow while the filter takes time for water to work through. Yes, the soft bottle seems like it'd be an idea for trail runners to use, but when it's empty, it is still pretty substantial because of the length of the filter, and you can't get enough water fast enough. The in-line compatibility with a hydration bladder is a great idea, but in use, it's slow and super hard to suck through. In gravity mode, it does work (after making sure all air bubbles are out), but all other gravity filters are faster than the Flex. While it is more durable and versatile, the Katadyn BeFree wins our Top Pick for lightweight travel because it has much faster flow rates, is lighter all-around, and is better to use for on-the-go missions.


Compare to Similar Products

Our Analysis and Test Results

The Lifestraw Flex comes with a 650 mL soft bottle and is compatible with in-line systems like gravity filters and hydration bladders. While we were excited about the idea of how functional this system could be, it has significant drawbacks in the form of filtration. It's tough to suck water through this filter, making it hard to recommend it for any of its many applications.

Performance Comparison


The Lifestraw Flex is a versatile system that offers versatility. Our biggest caveat that in every function it is super slow. From sucking water from the bottle to using it as a gravity filter.
The Lifestraw Flex is a versatile system that offers versatility. Our biggest caveat that in every function it is super slow. From sucking water from the bottle to using it as a gravity filter.

Water Quality


The Flex brought to you by Lifestraw filters out harmful bacteria and protozoa including Giardia and Cryptosporidium that occur across North America. It does not filter out viruses, so it is not for international travel where tiny viruses are a problem. Lifestraw also claims that it can remove lead from water sources.

This lightweight filter can get rid of most water-borne pathogens except viruses.
This lightweight filter can get rid of most water-borne pathogens except viruses.

The filter cartridge has a hollow tube design with an absolute pore size of 0.2 microns. This filter does work well in sediment-free water sources but has trouble when it comes to turbid water. It also features an activated carbon cartridge that improves the taste of water. The Flex has similar to performance to the Katadyn BeFree 0.6L except this filter does better with turbid water and doesn't clog easily.

The activated carbon and hollow filtration technology remove tastes  chemicals in addition to bacteria and protozoa. It does not remove viruses.
The activated carbon and hollow filtration technology remove tastes, chemicals in addition to bacteria and protozoa. It does not remove viruses.

Durability & Maintenance


One of our concerns with the Flex is in the durability of its bottle. Other soft bottles are notorious for ripping where the hard collar meets the soft, pliable bottle. That said, of soft bottles that we've used, the material is a lot thicker, and while it's collapsible, it seems to be more durable.

The filter screws into this coupling that can leak if squeezed too hard.
The filter screws into this coupling that can leak if squeezed too hard.

Another concern we have with the Flex is that the coupling between the bottle and filter leaks. When squeezed hard enough, some water comes out, which could potentially cause contamination.

The filter itself seems to be pretty durable but does get clogged easily. It is easy to clean. Unscrew and flush it out. You can also use a syringe (that doesn't come with the kit) to expel any air bubbles that are in the system that might clog it. The filter is good enough for 1850 liters or 500 gallons.

The Lifestraw Flex's bottle is 20oz capacity  so not great to treat a large quantity of water.
The Lifestraw Flex's bottle is 20oz capacity, so not great to treat a large quantity of water.

Treatment Time


Treatment time varies with the Flex given that it has many applications. As an on-the-go system, filtration is instant when the filter is on its own or in a soft bottle. This system also integrates into a gravity filter or an in-line system like a hydration bladder.

The Lifestraw Flex can be used for on-the-go hydration  but it takes time to suck what through its small output.
The Lifestraw Flex can be used for on-the-go hydration, but it takes time to suck what through its small output.

When we first tried to use this with a gravity filter, we hooked it up, and nothing happened. We waited for a while and wondered whether or not it works with an in-line system! After some YouTubing, we learned that the system needs to be completely free of air bubbles. So we used a syringe that came with a different product to clear the filter of bubbles potentially blocking air flow.


Upon doing this, it started to tickle and eventually released a steady stream of water. It took about 6 minutes to get 1L of water from a clear source in the end. The hydration bladder adaptation works but isn't practical given how hard you have to suck to get water. Though, it is instant delivery.

Weight & Packability


The soft bottle that comes with this unit can easily collapse into a smaller bundle about the size of a large salami sandwich. The filter can be used on its own (without the bottle) and has a slim profile that will fit nicely into a running vest or hiking backpack. It weighs about 3.60 oz making it a lightweight option, but not the lightest out there.

A look at the overall weight with bottle and filter.
A look at the overall weight with bottle and filter.

Ease of Set-Up


The Flex is easy to use. You fill the included bottle, screw in the unit, and squeeze or drink through the nozzle. If you want to use it with an in-line system, stick a tube from a gravity filter on the intake side. Or if you want to try it with a hydration bladder, you'll need to put a tube on both sides of the bladder or suck directly through the system.

Given that you need to scoop water, we suspect this could be harder to gather water from super shallow water sources. Everything else would work just fine.

Attaching the Flex's filter to a hydration hose. It feels like this may fall off if you let it dangle.
The Flex is easy to assemble  just fill the bottle and screw on the filter!

Ease of Filtration


Given the small intake and output on this filter, it's extremely hard to suck water through. In short, our main tester wouldn't choose this filtration system simply because of this fact.

You can also use it at the end of your hydration hose  but we found it difficult to get any water through.
You can also use it at the end of your hydration hose, but we found it difficult to get any water through.

Water needs to fill up the filter before you get any water which means working pretty hard for just a little sip. This issue almost makes the on-the-go idea functionless. We wouldn't choose it as our top choice for on-the-go travel simply because you have to work so hard to so little water flow.

You can still use the Flex as a straw style filter  but it is short and difficult to get down to.
You can still use the Flex as a straw style filter, but it is short and difficult to get down to.

Even with the soft bottle that we could squeeze to help facilitate the flow, we found ourselves working hard for just one sip of water. In a hydration bladder, the same trend occurs. As a gravity filtration system, it's slow, but this is the easiest way to use it, as long as you maintain it and it doesn't clog. Overall, this filter is c to use simply because the "sucking" requirement is exceptionally high.

Best Application


The Lifestraw Flex has a plethora of uses, but because of its slow flow, it's not our top recommendation. While the system does come with a hand bottle, we found that it was too hard to suck to make it realistically functional for trail running. The inline filtration is a great idea for hydration bladders, but again, because it's hard to suck, it's not that awesome to use. We do like for a gravity filter, although all the gravity filters we've tested have a much faster flow. It's ideal for trail running, backpacking, and the like, but it's simply not our top choice for most activities. There are better options out there for all applications.

On a ski trip  we test this system. It provided us with good on-the-go hydration while playing out in the mountains.
On a ski trip, we test this system. It provided us with good on-the-go hydration while playing out in the mountains.

Value


As a versatile system, $35 isn't so bad. If you can get over that you need to suck hard to get water, it's a good deal.

Conclusion


The Lifestraw Flex offers versatility. It operates on its own, in conjunction with a soft bottle, or with an in-line system like a gravity filter or hydration bladder. While it has a plethora of uses, we are seriously unhappy with its rate of flow that makes using it hard to use and quite annoying. It's not our top choice for any one application, but rather, works for many.


Amber King