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First Look: MSR HyperFlow Microfilter

by Dave MacLeay
August 4, 2008 first published January 16, 2008
MSR HyperFlow Microfilter

MSR HyperFlow Microfilter
Weight: 7.4 oz. (209 g)
Size: 7 x 3.5 in. (19 x 7 cm)
MSRP: $99.95
Available: Spring 2008

The MSR HyperFlow Microfilter is a lightweight, cucumber-sized water filter that utilizes hollow fiber technology to provide remarkably fast water filtration. Resembling a compact bike pump in form and function, the HyperFlow delivers up to 2 liters a minute and mates nicely with hydration bladders, Nalgene bottles, and even soda bottles.

The downside? It is susceptible to damage if dropped or exposed to freezing temperatures.


The HyperFlow’s claim to fame is its ability to filter water quickly: 3 liters per minute, according to MSR. In our tests, typical flow was about 2 liters per minute, although we never felt at a loss for capacity. Extremely aggressive pumping may provide additional flow, though we never felt the need.

More notable than raw speed is the HyperFlow’s capacity. It takes just 20 pumps of this little filter to fill a 1-liter Nalgene. But at only 20 strokes per liter, you’ll spend as much time switching between bottles as you will actually filtering. This little pump moves a lot of water and does it with significantly less resistance than many other filters.


MSR touts the HyperFlow as the lightest filter available, although the published weight of 7.4 oz. (209 g) is within a gram of the Katadyn Mini. Our test unit was slightly heavier at 8.2 oz. (232 g) for just the pump assembly, intake tube, and prefilter. The water bottle adaptor and carrying sack (with sewn-in instructions) add another 2.8 oz. (79 g) for a total packed weight of 11 oz. (311 g).


The HyperFlow’s 0.2-micron filter is effective against bacteria, protozoa, and particulate matter. Like all non-chemical filters it does not protect against viruses. The HyperFlow does not have a charcoal filter to treat chemical contamination, so water drawn from particularly dirty sources may retain some odor and/or flavor.


The prototype filter that we tested had some durability problems. Most notably the outflow coupling (which connects the filter to the water bottle adapter or hydration hose) broke under moderate strain during use. When filtering into a water bottle, the natural pumping motion can put a lot of stress on that area.

This was not a catastrophic failure – the filter itself still produced clean water – but pumping water into the open mouth of a Nalgene became somewhat awkward, it would no longer work for pumping into a bladder, and pumping into a smaller bottle was messy at best.

MSR says this problem will be addressed in production models. In the meantime, caution is advised: this is a lightweight product, and should be treated with appropriate care.

UPDATE (8/4/2008): Since publication of this review, we've had the opportunity to test a production version of the Hyperflow. Even under exaggerated stress -- beyond what one would expect during normal operation -- the production version did not experience the problems we had with the prototype. Click here for the full update.

Field Maintenance

Unlike some pleated and ceramic filter designs, the HyperFlow’s hollow fiber filter element cannot be cleaned by scrubbing. However, the filter is designed with a backflow mode, which allows you to pump clear water backward through the filter element, flushing sediments back out the intake hose. If the filter element becomes clogged with sediment, the filter can be disassembled and two check valves turned around to reverse the flow.

The process is documented on a card sewn into the HyperFlow’s carrying sack, but it can take a little practice to get comfortable with the procedure. There are a number of pieces to keep track of and the small check valve assembly can be difficult to grip to unscrew. It’s a good idea to practice this at home a few times before needing to do it in the field.


MSR designed the HyperFlow to attach easily to most common water bottles and hydration bladders. Hydration systems and small-mouthed water bottles or soda bottles can attach directly to the filter, and MSR provides an adaptor for 63 mm bottles (Nalgene or similar). The adaptor can replace the cap on one of your wide-mouth bottles and the “cap within a cap” provides a smaller opening that pours smoothly and prevents spillage. The small cap fits snugly, but can be a bit difficult to open and close. You can also pump into wide-mouth bottles effectively without the adaptor, but you’ll want to have a stable surface on which to place your water bottle.

Ease of Use

Operation of the HyperFlow is straightforward, and it requires very little effort to pump. Connecting the filter to a wide mouth water bottle using the adaptor takes a bit of figuring out the first couple times you do it, but once learned the system is straightforward. The adaptor cap itself can be difficult to open.

Because of its small size, the HyperFlow can be a bit awkward to grip – there just isn’t room for all your fingers. We consistently found ourselves with a couple fingers gripping the outflow coupling. Handling the output end of a water filter with dirty hands can contaminate the filter and introduce germs right back into your previously clean drinking water, so paying close attention to hygiene and how you’re holding the filter is essential.

The prefilter tends to float on the surface and can get more air than water if not placed carefully, especially in moving water. This can be a good thing, or a bad thing, depending on whether your water source is afflicted with loose sediment or floating surface scum. Luckily the Velcro straps that allow you to securely wrap the host and prefilter around the filter body can also be used to secure the prefilter to a branch or rock for more precise placement when needed.


The hollow fiber technology used in the HyperFlow allows for fast, easy filtering at a very light weight. The downside is that it’s relatively fragile. Exposure to freezing temperatures will break the filter element. When water becomes trapped inside the fibers (there’s no way to completely dry them) and it freezes, its expansion causes the fibers to break, rendering them permeable to the bacteria and cysts they’re supposed to be blocking.

MSR provides a test procedure that tells you whether or not a filter is still good. This procedure can be carried out in the field, without tools, by backflushing clean water through the filter and then checking the pump’s ability to hold suction and for the presence of air bubbles in the outflow. (Of course a still-frozen filter won't pump at all, providing an excellent clue that it’s broken.)

To test this procedure, we intentionally froze a filter element and then performed the filter test per MSR's instructions. The results were mixed. While the filter didn’t act quite like a new one, it also didn’t exhibit the behavior that the directions said would indicate a broken filter. This ambiguous “maybe-broken” result didn’t provide much confidence one way or the other. More indicative to me was that listening closely I could hear the sound of air being sucked through the filter element. When in doubt, it’s best to use a new filter element or a backup treatment method. It’s also a good idea to perform the test a few times with a known-good filter element so that you know what to expect and can treat any different result with suspicion.

If there’s any chance temperatures on a trip could fall below freezing, bring an extra filter element and/or backup treatment. Also be prepared to put the filter element in a snack-size Ziploc bag and keep it near your body – inside your sleeping bag or in an inside jacket pocket.

Bottom Line

The MSR HyperFlow is one of the lightest pump filters on the market, and by far the fastest. It is comparable in size, weight, and effectiveness to the Katadyn Mini, but significantly faster, at 2 liters-per-minute (tested) compared to the Mini’s .5 liter-per-minute ceramic filter.

Because of its cold-weather limitations and potential fragility, the HyperFlow is not for everyone. But warm-weather backpackers and lightweight hikers who can’t use chemical treatment, or simply prefer a filter, will find the HyperFlow to be a welcome option for three-season trips.