Mountain Hardwear Fluid 6 Backpack

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Manufacturer Description

This lightweight hybrid vest/pack offers ultra-runners and other endurance athletes a stable carry for hydration and gear.


  • Well ventilated wall mesh shoulder straps
  • Pocketing on shoulder straps provide quick access to energy bars, gel packs
  • OTF (On-The-Fly) Compression lets user adjust load stability while wearing the pack without restricting motion
  • Super stretchy mesh side pockets offer quick storage/access for water bottles or gear
  • Bungee helps secure overloads and compress pack’s load
  • Hydration sleeve pocket inside main compartment with dual ports
  • Reflective hits for high visibility and safety
  • Materials
    • Body – 100HT Ripstop Dobby Nylon
    • Accent – Hexwall Mesh
  • Capacity – 6 liters (365 cu in)
  • Measured weight – 270 g (9.5 oz)
  • Retail – $70

YMMV Review

Over the last couple years, Mountain Hardwear has begun to target the ultra running and long-distance running group.  They have mainly been making clothing to hit this market but recently released their first set of packs and gear for running.  The Fluid 6 is the smallest of the backpacks in this collection. Mountain Hardwear has always had a distinguished history in the alpine environment.  With their new foray into faster, lighter, and innovative products, they have also pushed into running which I am glad to see.  I have had good success with Mountain Hardwear since I got my first jacket in 2000.  I have been excited to see where this new focus on innovation will take them next.

Mesh Back Panel


I tested the Fluid 6 cross-country skiing and running.  My runs varied from 15 miles to 40 miles.  The runs were on both road and trail with weather ranging from 30 degrees to 75 degrees.

Design ★★★½☆

Appearance (10%) ★★★☆☆

Construction (40%) ★★★½☆

Pockets (20%) ★★★★☆

Sustainability (10%) ★★½☆☆

Weight (20%) ★★★★½

The Mountain Hardwear Fluid 6 is best described as a vest pack.  It is made to stay secure against your upper body for long-distance running when you need to carry a lot.  It only comes in one size but is made to work for men or women.  The Fluid 6 does not come with a hydration bladder, but it will work with virtually any of them on the market.  The pack has one main pocket.  In this pocket is a hydration sleeve with a hanger inside for your bladder.  There are two ports for the tube depending on which shoulder strap you would like to run the tube down.  Both straps have tube guides to keep the tube from bouncing around excessively.  The back panel is made of Hexwall Mesh for optimum breathability and strength.  The rest of the pack body material is made of Nylon Ripstop, which is superlight and weather resistant.  On the outside of the pack is a bungee system that can be used to tighten up the pack load as well as secure extra loads.  There is a clip at the end of the cord to allow it to be clipped out of the way rather than just having excess cord hanging off. This is a really smart addition to the pack.  The main compartment has a double zipper opening for easier convince to the inner goodies.  The pack holds 6 liters, which is more than enough for all my long runs.

Looking Inside, Hydration Sleeve

At the top of the pack, there is a haul loop for grabbing the pack.  The two shoulder straps are made of Hexwall Mesh for optimum breathability.  On these straps, there are bungee cords, which can be used to secure things like a hat or gloves.  There are even extra loops for adding other attachments you may have to the straps.  Mountain Hardwear does not sell any other attachments.  The shoulder straps have three pockets between them.  There are larger drop in stretch mesh pockets on both shoulder straps.  The left strap also has a smaller zip mesh pocket on the outside of the drop-in pocket.  The larger pockets are big enough for gels, nutrition, or even an iPhone.  The smaller pocket is ideal for salt tabs and other small items like that.  There are two sternum straps to keep the pack secure.  These straps can be moved up or down the shoulder straps with six possible locations.   The bottoms of the shoulder straps are connected to the pack by a v-shaped compression system.  This can be adjusted on the fly and is designed in a way to avoid restricting motion.  There is a fair bit of small reflective tabs on the front and back for visibility in low-light conditions.

Looking up the materials used in the construction of the Fluid 6, I was not able to find any information on the materials being green or sustainable.  Mountain Hardwear does have a code of conduct regarding a list of different manufacturing practices.  They address many of the aspects of social responsibility, which is good to see.  Their work toward being more sustainable does need a little work.

Front View

Fit ★★★★☆

Adjustability (20%) ★★★½☆

Comfort (50%) ★★★½☆

Ease of Movement (30%) ★★★★½

As a whole the Fluid 6 fits really well.  While the backpanel is just lightweight mesh, when the bladder is in there that provides some cushion between your back and the contents.  The mesh material itself is soft and caused me no issues even up to 40 miles of running.  The adjustable straps that wrap the body just above the hips are easy to adjust when on the run and do a great job pulling the pack in tight.  Unfortunately, these have a tendency to slowly loosen up when running so I got lots of practice tightening these straps.  Generally, I had to give them a pull about every two miles so it was not too bad.  I hope with more use the newness will wear off the straps, and they may stay more secure.  The sternum straps didn’t loosen as easily, but I would occasionally have to tighten them as well.  Between these straps, it is easy to get a fit that is comfortable and does not bounce.  The pack is definitely more comfortable when it is secured tightly rather than being loose.  Using the bungee cord in the back helps with that.  The bladder you choose to use will also greatly affect comfort.  I tried one that was too tall for the hydration sleeve, and it sloshed around quite a bit.  I settled on a 70 oz bladder as being the best choice.

Shoulder Strap Pockets

Performance ★★★½☆

Breathability (20%) ★★★☆☆

Durability (25%) ★★★½☆

Ease of Use (15%) ★★★☆☆

Reflectivity (10%) ★★½☆☆

Versatility (15%) ★★★★☆

Weather Resistance (15%) ★★★☆☆

The Fluid 6 has been a good running vest/pack for the most part.  What I love about this is the amount of carrying capacity the pack has.  Compared to other running vests I have this by far can carry more.  You can even bungee stuff to the outside if you deem it necessary.  On the contrary, the front pockets are slightly smaller than most running packs I have tested.  To add more storage, there are two side pockets that can be used for extra storage or even water bottles.  I used them for bottles when cross-country skiing as Melissa and I share them.  This is also why I really like the Fluid 6.  Not only is a good pack for running, but it can be used for other activities easily.  When cross-country skiing I tend not to use hip belts and like to carry less stuff so the Fluid 6 works much better than some of my larger options. The outer shell will block some weather and is better in the snow than the rain.  The drawback of this nylon shell is when you generate a lot of heat, I found that condensation can occur on the inside of the pack.  I was never enough to soak the contents but could make things a bit damp feeling. This did not happen on every run but did happen enough that it is a concern.

Side Pockets

I have not had any issue with the durability of the pack.  It has withstood every thus far.  I have seen some Mountain Hardwear sponsored athletes using these packs at races, and they look like they are still going strong even though they look well loved.  The Fluid 6 has some features on it and most are easy to use.  Making adjustments to the fit are as easy as pulling a strap.  The only challenging changes will be moving the sternum straps up and down.  Once you have figured out that technique, it is easy to duplicate.

Overall ★★★½☆

Overall, the Fluid 6 is a good pack.  I found it to be on par with many of the other running vests/packs on the market in comfort. Since it does not come with its own bladder you will need to try a couple to find one that works best for you.  The first one I used was too tall and made for a bouncy ride until I drank enough water.  Switching to a smaller bladder alleviated this problem.  The Fluid 6 is great if you need to carry a lot of stuff while running or want a smaller pack when doing other activities.  The low profile makes it well suited across a range of activities but does mean that it carries less on the shoulder straps than other running packs.  This is slightly made mute by the addition of the side pockets on the pack where more stuff can be made easily accessible while on the move.  These side pockets are also great for extra water bottles.  The fluid 6 can carry a larger load comfortably making it great for Ultra Distance events, or any other activities when you need a good range of motion and to carry some gear.  I would recommend taking a look at this pack if you are in the market, Mountain Hardwear did a good job here.  It retails for $70, but you will need to get a bladder if you want to use one.  As always, your mileage may vary.

Pros [field name=iFrame]

  • Lightweight
  • Carries a larger load than Competitors Packs
  • Comfortable, Snug Fit
  • Side Pockets help it be more Versatile
  • Can use your Bladder of Choice


  • Does not come with Bladder
  • Condensation can occur on the Inside of the Nylon
  • Straps occasionally loosen

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About the Author

I am an avid runner, cyclist, swimmer, hiker, climber, skier and many other activities that would make this list too long. I started Your Mileage May Vary Reviews in Early 2011 to combine two of my passions: sports and gear.

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