Reader question: Is the Flex Capacitor Pack appropriate for a thru-hike?

From Lisa K.:

Why do you say that the Flex Capacitor is best for 3- to 7-day trips? I am preparing for my first thru-hike, and am seriously considering this pack. Can it be used for thru-hiking?

For two reasons I wanted to share my answer to this reader question.

First, I have not yet addressed the appropriateness of the Sierra Designs Flex Capacitor 40-60 Pack for thru-hiking, and I probably should.

Second, it gives me an opportunity to discuss the specific needs of thru-hikers in regards to backpack selection.

Appropriateness for thru-hiking

The Flex Capacitor can most definitely be used on a thru-hike. It’s durable and lightweight; its feature set and its volume are in the sweetspot; and its max comfort weight is adequate, if not excessive.

I think the Flex will perform especially well on long-distance trails with:

  • Heavy food loads, due to infrequent resupply points;
  • Heavy water loads, due to arid conditions;
  • Heavy base weights, due to inclement conditions or multi-use equipment; and,
  • Bear canister requirements.

It would be perfect for the John Muir Trail, for example, because canisters are required along most sections of the JMT and because resupply opportunities are far and few between. It would also be ideal for southern sections of the Appalachian Trail in February and March, when cold-and-wet conditions encourage the carrying of extra clothing, a warmer sleeping bag, and a heavier stove system.

Even when these conditions do not apply, I think many thru-hikers will appreciate its load-carrying capacity and adjustable volume. Most thru-hikers do not start with minimalist loads, and many stick with “ultralight plus” kits because they enjoy having a few luxuries or toys.

For what type of thru-hiker would I not recommend the Flex? Basically, the reverse of the aforementioned scenarios — so frequent resupplies, abundant water, benign conditions, no bear canister requirements, and a streamlined kit.

Pack specs for thru-hiking

What a thru-hiker needs from a backpack is not necessarily any different than what is needed by a non-thru-hiker.

The average thru-hiker probably carries less than the average non-thru-hiker, so thru-hikers generally use smaller and less supportive packs. But, plenty of non-thru-hikers carry loads that are as light as the lightest thru-hiker. And, actually, non-thru-hikers can more easily carry less, because they can cherry-pick the conditions.

Moreover, I don’t think that thru-hikers and non-thru-hikers vary in their expectations of durability, comfort, and features like external pockets, reservoir sleeves, and compression.

A final non-difference is the respective duration of thru-hikes and non-thru-hikes. A thru-hike is simply a connected series of bite-sized trips, each of which start and stop with a resupply.

Just like non-thru-hikers, a thru-hiker normally leaves town with 3 or 5 days of food in their pack, and 7 or 10 days is considered exceptional. This means that thru-hikers and non-thru-hikers both need a pack with about the same amount of volume and load support, assuming their backpacking style and the environmental conditions are similar.

Learn more about the Flex Capacitor Pack

Posted in on February 13, 2017


  1. James W on March 9, 2017 at 9:19 am

    Andrew, I am considering the Flex Capacitor. Regarding the 70 lb tested weight…what is the comfortable usage max weight in your opinion? I have a UL pack listed to <40 lbs. Realistically it's 35 and that might be a stretch, maybe to 40 in a short term – one of. The pack that will work to KM, but figure that it's not a 40 lb comfortable carry for the potentially slow conditions that one might expect early this season in the Sierras, when I have to add more food and some heavier items. Thanks.

    • Andrew Skurka on March 10, 2017 at 9:47 am

      Generally speaking, it will comfortably carry the weight that you can put in it, assuming a normal backpacking load of gear, food, and water.

      In November I was out for 5 days with a 40-lb load, including an 8-lb rifle strapped to one side, and thought it did really well. If I’d had spare volume, it could have held another 5-10 pounds before nearing its limit. I don’t have much of an upper body (in terms of muscle or natural padding) and most people will find a pack more comfortable than me.

      The Y-Flex suspension is extremely stiff and is anchored directly into the hipbelt, so the weight transfers extremely well. It’s excessive for lighter loads, but the suspension is so simple that there is no weight penalty. The bigger issue is that this stiffness translates into less mobility, which some might interpret as comfort.

  2. Tom M on March 15, 2017 at 2:47 pm

    Hi Andrew,
    I’ve watched your packing video with the FP pack. How might you incorporate soft items around a bear can will still keeping them waterproof? Would you put the can in trash compactor bag? Or just put the wet stuff around the bear can like the tent, hard shell, etc. and then put your next compactor bag on top?

    • Andrew Skurka on March 15, 2017 at 9:01 pm

      I keep wet items outside the pack liner, but inside the backpack. The bear can stays inside the pack liner with other dry items.

  3. Damien on April 19, 2017 at 6:20 pm


    this is regarding both your tent system and the flex capacitor; any suggestions on how to get to see them in person and ‘try them on’ before buying? I checked the Sierra Designs website and the retail outlets options they have are somewhat limited. I live in Boston, MA, and the nearest retail outlet for Sierra Designs listed is in NYC. Is the tent system still in production? The Sierra Design website has it being out of stock?

    • Andrew Skurka on April 19, 2017 at 6:28 pm

      A few options:

      1. Buy it and, if you don’t like it, return it. I don’t know exactly how SD or its limited dealer base handles returns.

      2. Call up a local SD dealer and ask them if they could special order it. If you don’t like it, you could return it to them.

      The tent is still in production. We just sold through our inventory. More are on the way.

  4. RamboJuice on November 14, 2017 at 3:51 pm

    I used my Flex Capacitor on 1400 miles of the PCT and it performed great. Smaller when you need it small, large when you needed it large. This backpack has great airflow for your back which is a huge advantage in my opinion.

  5. Momo Mora on April 9, 2018 at 2:09 pm

    Hi Andrew,
    As I am about to thru-hike the JMT SOBO (late August) I am actively shopping for my “perfect backpack” and I just run into the “Flex Capacitor”. Everything about it seems to fit what I’ve been looking for, lightweight, capable of handling heavier than 40lb-loads, able to hold/fit bear canisters, great lumbar support, among others. However, I noticed on the “Section Hiker” review of this pack that it was listed as “Men’s Only”. Would the Flex be suitable for women as well? (I am 5’6″, 136lbs, estimated base weight: 25lbs). Thanks

    • Andrew Skurka on April 9, 2018 at 2:27 pm

      Unless Philip can metamorphose into a woman, I think it’s presumptive to say that the Flex is only for men.

      Packs are kind of like shoes, in that there is consideration for fit. The Flex will fit torso lengths of 16-21 and straighter-shaped bodies. On average, it will fit men better, because their torsos tend to be in this range and because they have less differential between the girth of their waist and hips. But it fits well women who are taller and less hippy than average. If that’s not you, then you might want to look at a woman-specific pack, which will have a more aggressively angled hipbelt and narrower shoulders.

      • Momo Mora on April 9, 2018 at 6:41 pm

        Thank you so much, Andrew, for your prompt response, very much appreciated.

        Never implied that someone would’ve had to go through any type of transformation. On the SD website, under the product description, it doesn’t specify anywhere that it’s gender-specific or that it’s only suitable for specific body types. That would’ve definitely helped during my research, or anyone else’s for that matter. It’s hard to guess those details.

        Thanks, again, for the additional information.

  6. Keith Kitchen on March 20, 2019 at 12:11 pm

    Hi Andrew!

    I purchased a Flex Capacitor and used it on a couple of trips last summer. Great pack, overall.

    Over the past few years, I’ve been steadily refining my gear choices and have been able to whittle down my base weight to around 11lbs without sacrificing safety or comfort. Typical use for me is a 5-7 day trip in the Rocky Mountains (GDT) with a total weight currently around 25lbs.

    I’m cdebating whether or not to switch out my FC in favour of a lighter, frameless pack. (Something like the MLD Burn or Prophet.) The FC, as you know, weighs around 2.5lbs, whereas these frameless options weigh a little over a pound. The FC is by far the heaviest item on my gear list and the opportunity to cut a pound and a half with just one item is significant and tempting.

    If the question is simply a numbers game, it’s a no-brainer, but I suspect there’s a difference between actual and perceived pack weight. In other words, a 27 lb loadout with the FC may feel lighter than a 25lb loadout with the MLD pack. In which case, I’m better off as I am.

    The secondary question is where the law of diminishing returns kicks in. Is it worth it to go through the hassle and expense of selling and buying a new pack to shave 1.5 lbs.

    Appreciate whatever light you can shed on this.

    Sincere thanks.

    • Andrew Skurka on March 21, 2019 at 8:49 am

      The weight-savings of a frameless pack are tempting, but there’s a big tradeoff. A frameless pack does not carry heavier loads as well, and it’s not nearly as comfortable if you ever need to carry a bear canister.

      If your starting pack weight is 27 lbs, I would not swap it out. I think you want to be regularly below 20 lbs before you make that switch. Maybe the first day or two you’re above, or when you tank up on water, but most of the time you’re below.

  7. Gabriel Ortiz on July 31, 2020 at 12:32 am

    Hi Andrew I will hike the JMT on late September, I m not sure what’s better to fit gear (tent plus bear canister, is the 40-60 enough or 60-75 is too much?

    • Andrew Skurka on July 31, 2020 at 8:41 am

      The best way to measure needed pack volume is to put all of your stuff in a box, and measure the dimensions of the filled space.

      That said, I can give you a little bit of perspective about pack volume on the JMT at this time of year. I frequently have guided trips in late September in the High Sierra, up to 7 days in length while carrying a beer canister. The 40 to 60 liter pack should be sufficient so long as the rest of your kit is reasonably streamlined. If you’re carrying a lot of junk and heavy gear, you will probably need the larger version.

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