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Reviews > Hydration Systems > Bladders > Polarpak MOFLOW Hydration System > Test Report by Kurt Papke

Polarpak MOFLOW Hydration System

Test Series by Kurt Papke

Initial Report - August 6, 2008
Field Report - October 1, 2008
Long-term Report - November 25, 2008

August 6, 2008

Tester Information

Name: Kurt Papke
Age: 54
Gender: Male
Height: 6' 4" (193 cm)
Weight: 220 lbs (100 kg)
Email address: kwpapke at gmail dot com
City, State, Country: Minneapolis, Minnesota USA
Backpacking Background: Mostly in Minnesota - have hiked all of the Superior Hiking Trail and Border Route.  Preferred/typical  backpack trip is one week.  Some hiking in Utah, Colorado, North Dakota and Oregon.  Mostly Spring/Fall seasons.  Comfort-weight hiker: I try to carry as few items as possible, but do not go to extremes to reduce weight of items carried.  Because of my physical size & weight I consume a lot of water when I hike, at least 1 gallon (4 liters) per day including meals, even more in hot, arid conditions.

Initial Report

Product Information

Manufacturer: POLARPAK
Year of manufacture: 2008
Manufacturer website:
Listed weight:  N/A
Weight as received: Reservoir with hose & bite valve: 6.1 oz (174 g)
Pump: 1.23 oz (35 g)
Shower attachment: 3 oz (84 g)
Listed Dimensions:
Capacity: 70 oz (2.07 l)
Reservoir dimensions: 6.75 in x 15.2 in (17.15 cm x 38.6 cm)
Measured Dimensions:
Capacity: 59 0z (1.75 l)
Reservoir dimensions (empty): 7 in x 15.5 in (17.8 cm x 39.4 cm)
MSRP: Reservoir: $31.95 US
Shower attachment: $14.95 US

Product Description

Moflow reservoir and showerhead in packageThe Polarpak MOFLOW hydration system was received in two packages:

1. (right in picture) The reservoir, supply tube, bite valve and pressure pump
2. (left in picture) A shower head accessory system

MOFLOW is a moderately-sized (2 qt/l) water vessel that can be put under pressure to facilitate drinking.  The pressure reduces the need to suck from the bite valve when drinking in the field.  According to the Polarpak website the pressurization encourages the hiker to drink up to 30% more water, and thus in theory to stay more hydrated.

The reservoir is filled from a water source by unscrewing the large orange cap which is visible in the photo at left.  Once filled, the cap is screwed back on.  In my initial tests I found very little torque was required to get a water-tight seal with the screw cap.  Note in the product information above that I was only able to fill the reservoir to about 85% of the manufacturers listed capacity.  It may be possible to attain the full 70 oz (2 l) of water, but I was not able to do so before spilling lots of water.

Next the supply hose is connected to the exit port coupler at the bottom of the pack with a 90-degree twist motion.  I found connecting the hose to be straightforward, and I received positive reinforcement of a proper connection when the connector popped out very slightly when engaged, and will not unscrew without pressing in on it.

MOFLOW with pump connectedNext the pump is connected (before the bite valve is) as in the picture at left.  Note that there is also an option to connect the pump directly to the exit port without using the supply tube.  The bulb is squeezed 60-80 times forcing air into the reservoir.  I found with a full bladder that 80 squeezes gave me very tight pressure.  Any more pumping beyond this caused pressure to bleed from the pump, making it difficult to over pressurize the system.

Once pressurized, the pump is detached and replaced with the bite valve.  Note that unlike most reservoirs the MOFLOW has valves at both coupler joints that prevent water and air from escaping.

To drink from the system, bite down on the valve with the teeth, or (in theory) squeeze with the fingers to squirt water into the mouth.  No matter how hard I tried with my fingers, I could not get the bite valve to squirt unless I bit down on it.

MOFLOW showerhead attachedShowerFor use as a shower, the bite valve or supply tube is disconnected and replaced with the shower head/tube assembly as shown in the photo at left.

The resultant shower from the head is shown in the photo at right.

Showerhead valveOperation of the valve on the shower head took me a few moments to figure out as there were no instructions with it, but its really quite simple: pull the head itself and a slide valve as shown in the photo at right allows water through the head.

Polarpak states that the entire system is made with Microban antimicrobial material which obviates the need to clean the system with bleach.  In fact the instructions expressly forbid the use of bleach on the system components, and recommend rinsing with a salt solution.

HangersHanging/packing: the reservoir has two hanger slots at the top corners.  I have a daypack that has a hydration sleeve and hangers for a hydration pack, and I found that the reservoir fit the sleeve nicely and mated well with the hangers (see photo at left).

Initial Impressions

Usability: Polarpak has made this system as simple to use as possible, given that it requires more connecting/disconnecting of valves and pumps than most hydration systems.  The shutoff valves in the exit port and supply tube make the pressurization of the reservoir painless, and avoid wasting precious water in the field.

Bite valveOne potential usability concern is the lack of a clip for attaching the supply tube or bite valve to a pack shoulder strap.  In the photo at left a small hole in the bite valve assembly seems like it might be able to be used to attach to a shoulder strap with some elastic bands, but I'll have to play with this in the field to see how it works out.

Capacity: my "kitchen tests" seem to indicate that maximum pressurization of 60-80 squeezes will not allow evacuation of the entire reservoir.  My experience was about 60-70% use before it ran out of pressure.  Note that this is not a serious issue, as mouth suction can be used to drink just as with a non-pressurized system.

Flow rate: with a full reservoir and pressurization, I found that the system would deliver about 50 ml (1.7 oz) of water in 10 seconds.

Test Plan

  • Accessibility: do I find it convenient to access the pump to repressurize while on a hike?
  • Reliability & robustness: any leaks? Does the bite valve get teeth marks from me biting down on it?  Any wear and tear on the connectors?
  • Functionality: do I really drink 30% more water with a pressurized system?  In an arid climate this may not be a good thing, as I could burn through my water faster than I wish.  How well does the Microban prevent mildew or funky odors from forming?  Can I really wash my hair (or maybe even more of me...) with the shower head?
  • Aesthetics: how do I feel about pumping up the unit in areas where other people are present?  Do people ask me if I'm taking my blood pressure?
  • Packability: do I find the pump and shower units stow easily?
  • Weight/benefit ratio: the MOFLOW adds some weight over a traditional reservoir with the pump and (optional) shower head.  After several months of use do I find that the weight and space consumed are worth the upsides?
  • Polarpak also claims the reservoir can be used as a pillow.  Makes sense, as it can be pumped to any desired hardness.  I am excited to try this in my Hennessey hammock, as I've long wanted a pillow, but didn't want to carry the extra weight.  It'll be interesting to see how well this system multi-tasks.
This concludes my Initial Report on the Polarpak MOFLOW hydration system.

Field Report

Field Information

My principle use of the MOFLOW was on a 1-week backpacking trip to Isle Royale National Park in Michigan September 8-14.  Temperatures during this trip ranged from a low of 40 F (4 C), to some daytime highs around 75 F (24 C).  Altitude ranged from a low of about 620 ft to a high of 1371 ft (190 to 420 m).  Terrain ranged from swampy lowland to granite ridgelines.  Daily mileage ranged from 5-13 miles (8-21 km).  Water for the hydration system was purified from lakes with a pump filter system.

Packing Information

MOFLOW in sleeveI carried the MOFLOW reservoir in the hydration sleeve of my Mountainsmith Boundary pack.  As can be seen from the photo at left, the MOFLOW is tall and narrow, and my pack sleeve seems more designed for a shorter but wider reservoir.
Even though the reservoir extended up well beyond the sleeve, it fit in the pack.  The bite valve and tube were easily fed through the hydration system openings in the pack.

I carried pump bulb and showerhead in the packlid where they were easily accessible without having to open the pack.

MOFLOW clipped to shoulder strapThe MOFLOW did not come with a clip for attaching the tube/bite valve to my pack strap for easy access.  I improvised and borrowed the clip from another hydration system as can be seen in the photo at right.  This worked great and kept the bite valve accessible.

Use as a Shower

One of things I like to do after several days on the trail is wash my hair.  On Day 3 of the trip I broke out the MOFLOW showerhead, filled the reservoir with water, and tied the reservoir to the support rope of my hammock:
MOFLOW tied to hammock
Though the reservoir was fully "pumped" with air, I found that to get decent showerhead pressure some gravity was needed to assist, and my hammock provided a good spot to get it elevated.  The hanger slots in the reservoir worked well for looping a hanging rope through.  I found that I could shampoo my hair with about half of the water in a full reservoir.  After I finished, I turned the system over to my hiking buddy who can be seen using the unit to shampoo his hair in the following photo:
Shower system in use
This all worked quite well, and made us feel clean and refreshed.

Use for hydration

Filling the reservoir

The first difficulty I ran into with the MOFLOW was filling it with purified water from my filter system.  This presents several challenges:
  1. The shutoff valves on the supply tube are incompatible with my filter
  2. The fill opening is incompatible with the adapters my filter system supplied - the opening is just a bit smaller than a standard wide-mouth Nalgene bottle
  3. If the reservoir is set horizontally on the ground the water flows out of the opening
  4. The reservoir is too limp to stand up vertically while filling
The solution I found through trial-and-error was to use my empty Gatorade bottles as an intermediary.  Their mouth exactly matched the opening on the reservoir, so by filling two 1-quart (.95 l) Gatorade bottles and dumping them into the reservoir I had a good fill.


My first use of the MOFLOW was along the Minong Ridge trail on a fairly cool day, where I was concerned that I wouldn't drink enough water and hoped that the pressurized hydration system would encourage me to drink more.  That strategy was successful: by noon I had emptied the reservoir.  I had to re-pump the system about half-way through the supply of water to maintain pressure.  During the day I found the system very easy to use: just bite down on the valve and my mouth quickly filled with water, more than I would normally drink from a hydration system.  I attribute this to the lack of effort in drinking: normally with most systems I have to "suck" the water through the bite valve, but drinking from the MOFLOW was effortless.

The Leak

The second use of the system was a rainy day, hiking from Little Todd Harbor to Hatchet Lake.  After an hour or so on the trail I noticed that the bottom of my pack was quite wet, more than I would have anticipated given that it was not raining very hard (yet).  I had my rain jacket on and my gear in waterproof stuff sacks, so I didn't worry too much.  A few hours later I observed that the reservoir was empty, even though I had not drank all that much.  I guessed that the system had developed a leak, but I didn't know where or how.

When I returned home I did a standard test for a leak: inflated the reservoir and submerged it in a tub of water to check for bubbles, and as can be seen in the photo below the system had developed a leak at the tube/reservoir connection point:
Bubble, bubble, its trouble
By wiggling the tube I determined that the leak would only occur if there was pressure down on the tube/valve assembly - if it was left to float free it did not leak.

I contacted PolarPak customer service, and they did not have a replacement unit in stock to send to me.  They promised to send me a replacement O-ring for the drinking tube fitting, as that is the failure point they have seen, and received a lifetime supply (10) of O-rings three days later.  I asked them if I should superglue the fitting to permanently seal it to continue to test if the O-ring did not solve the problem, and they agreed that would be the best path forward.  I replaced the O-ring, and it slowed the leak, but did not stop it completely.  Looks like the rest of the test will be done with a superglued fitting.

Use as a pillow

I like to use a pillow when I sleep on my side in my hammock.  The following picture shows the MOFLOW wrapped in a cotton T-shirt to make it more comfortable, positioned at the head end of the interior of the hammock:
MOFLOW as pillow
I found the fully-inflated MOFLOW made a very comfortable pillow for side-sleeping, though I did notice my ear hurt a bit in the morning, so I may have over-inflated the pillow and made it too hard.  The rectangular shape of the MOFLOW made it easy to orient the "pillow" in different directions depending on how much support I was looking for and how I was laying.  I let some air out of the reservoir and tried it again the next night, and it made a huge positive difference.  Properly inflated, this makes a great pillow.


  1. Positive water pressure encouraged me to stay hydrated.
  2. Showerhead was a pleasant way to keep my hair clean.
  3. Nice pillow, great multi-tasking!
Areas for improvement:
  1. No leaks!
  2. Make the system easier to fill.  Either the fill opening should be the same size as a standard wide-mouth Nalgene bottle, or supply a fitting compatible with a filter hose.
  3. I cannot pressurize the reservoir enough to use the entire contents without re-pumping.
  4. The size of the reservoir is not big enough for me to shower my entire body - I run out of water when I try to rinse the soap off.

Long Term Report

Field Locations/Conditions

Moflow on the SHTDuring the Long Term Report (LTR) period my principle use of the MOFLOW was on a 4-day backpacking trip along the Southern end of the Superior Hiking trail in Northern Minnesota from October 13-16.  This trail section varies in altitude from 650 to 1200 ft (200 to 365 m).  The terrain is forested with granite outcroppings.  Temperatures ranged from a high of 60 F (16 C) to a low of 28 F (-2 C) at night.

The MOFLOW is pictured at left with the Gatorade bottles I used to fill it during the trip, and the filter I used to purify the water.  The rivers and streams I fetched water from were very high in tannins, which my filter does not remove.

Prior to departing on this trip, I superglued the fitting between the drinking tube and the reservoir to permanently stop the leak.  This was effective, but also meant that I could not disconnect the drinking tube and had to take it with me when filling the reservoir as can be seen in the photo.


  • I used the MOFLOW extensively during this trip, and became accustomed to the pressurized water flow.  I stayed well hydrated during the cool weather, which I credit at least in part to the ease of drinking from the MOFLOW system.
  • The water I filled the MOFLOW with during this trip had a lot of tannins in it.  The MOFLOW was resistant to staining from the water and I could detect no off-flavors after filling the bladder with tap water when I returned home.
  • Precisely because I became accustomed to the pressurized water delivery, it became more irritating to me when the MOFLOW ran out of pressure while it still had plenty of water remaining.  When there is no pressure in the reservoir, the MOFLOW requires a fair amount of effort to drink from.
  • On one occasion I re-pressurized the reservoir when it was nearly empty, though I was not aware of that condition.  After drinking a few mouthfuls of water, I got a blast of air injected into my stomach.  I discovered that the MOFLOW can be a very effective device for inducing belching.  This experience made me a little wary of using the MOFLOW when I was not sure that it was fully topped up with water.  This is actually a consequence of one of my general gripes with hydration bladders, I cannot see how much water is left in the system without removing it from my pack.
  • The necessity of carrying Gatorade bottles with me to refill the reservoir became irksome.  I never seem to have enough hands when I am pumping water, and the need to carry an extra bottle just because I could not fill the MOFLOW directly irritated me after a while.
  • I did not carry the showerhead with me on this trip. The temperatures were pretty chilly.
  • I often ended up drinking from the system after the pressure was depleted.  It is a pain to stop hiking, take off my pack, dig the pump out of the pack, disconnect the bite valve, hook up the pump, pump up the reservoir, disconnect the pump, stow the pump, put the bite valve back on, and put my pack back on.


My bottom line after testing the MOFLOW for 4 months is that I am unlikely to continue to use the system in its current design configuration.  The critical issues for me in priority order are:
  1. I don't trust the fittings.  I don't want to carry a system that I am worried is going to leak.  Gluing the fittings solved the problem during the Long Term Report period, but I am concerned that the glue could fail with age or cold temperatures.
  2. The value of the pressurized water delivery for me is not worth the additional weight, bulk, complexity and pumping effort.
  3. The problems with filling the reservoir have nothing to do with the pressurized system, but nonetheless I find filling the system very inconvenient.
  4. The showerhead adds little value, but does add weight and bulk to my pack.  I am able to shower or wash my hair using a standard unpressurized reservoir using gravity and its drinking tube.
I see great value in having a hydration system that encourages people to stay hydrated.  If Polarpak can address some of these issues in future revisions of the product I think they would have a product I would buy.

This concludes my report on the Polarpak MOFLOW Hydration System.

Many thanks to Polarpak and for the opportunity to test this product.

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