Hollow Fiber Backpacking Water Filters - what are they and how to take care of them

filled Vecto next to 3 different Sawyer filters and a Hydroblu Versa Flow

Hollow fiber backpacking filters use a very simple mechanical process to separate water from any bacteria, protozoa, or microbial cysts, and thus filter the water.

The most important factor of a hollow fiber filter is the size of the pores that it has, usually measured by microns. The smaller the pores are, the more particulates they remove from the water and the cleaner the filtered water is. But how does the hollow fiber filter work?

Various filters

The Mechanism of a Hollow Fiber Filter

  • Closed-loop hollow tubes with pores that are open towards the "incoming" side of the filter.
  • Water is "pushed" into the hollow fiber.
  • Water in the tubes is "pushed" through the pores.
  • Bacteria, protozoa and cysts bigger than the pores remain in the fiber.

This process means that the hollow fibers are being filled with "gunk" (bacteria, protozoa, cysts, mud, dirt, sand, etc) that blocks the pores over time. This is why all hollow fiber filters require regular backflushing.

How To Maintain a Hollow Fiber Filter


Backflushing is when clean water is pushed through the filter's outlet into the hollow fibers through the pores. Backflushing pushes out any residue that got stuck in the hollow fibers and cleans the filter, increasing flow rate and efficiency.

Backflushing is not enough to really clean the filter. A good tap (or 5) on a hard surface will help dislodge any sediment from the latest trip. 

The best way to backflush is to use a big container (like a Smartwater bottle or a Vecto), flush a bit, tap the filter on a hard surface, flush again and tap some more. Repeat the process until the water coming out is clear. 

It is recommended to backflush after every 2-3 days of backpacking and after every trip. If dealing with really bad water conditions (check our Hydration Horror Stories), clean your filter daily.

Freezing Conditions

Hollow fibers filters' biggest Achilles' heel is freezing conditions. Because filters actually have water in them, when that water freezes it expands in the hollow fibers and splits them, essentially ruining the filter.

To prevent the destruction of a filter, keep it above freezing level by keeping it in your sleeping bag on sub-freezing nights and in your jacket when hiking in cold conditions.

Storage tip: if you have an empty Vecto with you, store your filter in the Vecto to prevent your sleeping bag or jacket from getting wet from the filter.

 Sawyer Mini in Vecto

Whether you are using a Sawyer filter (Mini, Squeeze or Micro), a HydroBlu (Versa Flow), LifeStraw, BeFree or any other similar filter, look for a pore size not bigger than 0.2 microns, but 0.1 or smaller is better.

Maintain well and pair it with a Vecto for the best performance.


  • Kenneth Scholz

    Baking soda doesn’t disinfect. Use chlorine bleach (without other chemicals, check) or hydrogen peroxide per mfgr’s instructions – both kill about everything and evaporate without residue.

  • Gilad (Cnoc Outdoors)

    Hi Linda, if you suspect that a filter split due to freezing, I’d recommend replacing it as there is no viable way to actually check.
    In terms of cleaning and maintenance, you can backflush and clean a filter at any point, you probably don’t have mold inside, only dirt and dead bacteria. To be on the safe side, instead of using Chlorine, use 2 tablespoons of baking soda in 1 liter of warm water to backflush. Make sure you tap the filter to dislodge any particles that might block the filter.

  • Linda Selover

    How can you tell if your filter has been ruined due to freezing?
    Also, if you did not rinse it out after getting home, can you soak it in water w/ bleach to clean it, or should I just toss them out?
    After both of my long treks on t he JMT, it took me several days to get home, so I never took them out to clean them.

  • David Sachs

    It would be nice if Sawyer made an adapter to couple their filter to a garden hose. That way all one would have to do is connect them and let the water run for awhile…Just a thought.

  • Karen Wolfer

    Excellent instructions. Have never seen such clear visuals anywhere else. Thank you!

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