Gear Review: Sierra Designs Flex Capacitor Backpack

with 2 Comments
Flex Capacitor backpack on the PCT in the Sierras

Sierra Designs put together a great backpack.  The Flex Capacitor offers comfort, ample space, and durability.   All packaged into a smart design with the assistance of well-known thru-hiker Andrew Skurka.  This pack is a great choice for a thru-hike because of its simple design, toughness, and lightweight design.

Simple Design

The Flex Capacitor is a single compartment style backpack.  The main compartment is accessed by 1 large zipper on the lid on the top.  Unlike other single compartment style backpacks, you do not have to roll the top.  The lid is a zippered pocket.  It is great for storing items you want easy access to without unloading your entire pack.  The Flex Capacitor has 2 large hip belt pockets and 2 mesh elastic side pockets.  The side pockets are easy to access without removing the pack.  We kept our two one liter Smartwater bottles in them.  The water bottle pocket is on the right shoulder strap.  We used this to hold our GPS or phone.  This is a very clean and tidy backpack.  I think that having fewer pockets on the outside will help keep your items organized and force you to pare down what you bring on the trail.

Lightweight with Large Capacity

The Flex Capacitor goes from roughly 40-60 liters.  You can adjust the side straps to decrease the size and keep items from shifting.  The small internal frame is really just some DAC poles and offers great support.  The Flex Capacitor weighs in at 2lbs 11oz, for the large size.  This was a great size for the PCT because we could decrease the size when we only had a few days between resupply points.  Once in the Sierra mountains, we were able to easily fit a BV500 bear canister into the pack.  Some comparable packs weigh a bit less; therefore, also carry less. So if you are pushing the limits, this makes more sense.


The Flex Capacitor was a very comfortable pack to wear.  I had no problems adjusting the pack to fit properly.  Adjustment straps for the shoulders are easy to reach with the pack on.  The hip belt padding was sufficient and in the proper place.  One of the best features of this pack was how breathable it was on my back.  There is tons of space between your back and the pack, thus allowing air flow, like no other pack I have tried on before.  Most other packs that I saw on the PCT did not even compare to the air flow you get from the Flex Capacitor.   The Flex Capacitor comes in different sizes with a changeable hip belt to fit your body.


I used this pack for 1,400 miles on the PCT and did not have any issues with it that I would not consider wear and tear.  I used the Flex Capacitor as a back support to sit up against most days when we stopped for a break.  The sun only slightly faded the backpack after months of abuse.  All zippers on the pack are heavy duty.  Light-duty zippers tend to fail on the PCT because of the dust in the desert section.  We personally saw this on one of our tents.


This is a great backpack for the money!  I was completely happy with this pack on my hike through 1,400 miles on the PCT. The Flex Capacitor is a very tidy and neat package.  All the pockets and pouches are great sized and easy to reach while hiking.  I sweat a bunch. The Flex Capacitor tended to keep me drier on my back than others would have.  If you are wanting to shave every single ounce you can, this is not your pack, but if function and comfort are worth a little extra weight, this may be the perfect pack for you to try.  Also if you are looking around at other packs in this weight range, consider everything most advertised weights don't include a brain, hip pockets, water bladder inserts etc.  This is the full weight listed and is pretty good at that weight.

See the Flex Capacitor here.

See our Full Gear List here.

2 Responses

  1. Jan
    | Reply

    I currently own an Osprey Atmos 65 that squeaks a lot when hiking with it, does this pack tend to that? Also, I notice looking at pictures of the Flex Capacitor pack that the lumbar support protrudes quite a bit to give you the airflow. Did you find that uncomfortable at all. I tried a ULA Circuit pack that was a similar design in that regards. Also, were you able to pull out a water bottle and put it back into the side pocket easily when hiking?

    • RamboJuice
      | Reply

      I did not find that this pack much noise. The lumbar support is very comfortable. We carried 2 smart water bottles on each side and were super easy to access and unlike some other packs I have had the bottles did not fall out when bending over. I thought that this pack was very comfortable and designed very well, only thing I wish it had was on outside mesh.

Leave a Reply

Your email address will not be published. Required fields are marked *