Top

Room for improvement: Self-critique of the Flex Capacitor 40-60 Pack

On the summit of James Peak with the Flex Capacitor, the fifth and final 13'er of the day, looking south towards Bancroft, Parry, Eva, and Flora.

On the summit of James Peak with the Flex Capacitor, the fifth and final 13’er of the day, looking south towards Bancroft, Parry, Eva, and Flora.

Recently I highlighted seven standout specs and features of the Sierra Designs Flex Capacitor 40-60 Pack. Today, I’ll do nearly the opposite: identify its imperfections.

Since I co-developed the Flex Capacitor with Sierra Designs, naturally I want to see strong sales of it. But I also want prospective buyers to understand its optimal applications and tradeoffs, and ultimately find the best backpack for them. All else being equal, I hope you will support my forthrightness.

1. Limited sizing and color options

A limited production run will become available in October, directly from Sierra Designs. Sign up for updates. It will come in one color scheme and three unisex torso-length sizes (S, M, and L).

The color option will not change for retail distribution in spring 2017, but sizing will. It will consolidate to unisex S/M and M/L, which will still have 3-inch ranges but which will cover most of the market with one less SKU.

These limited sizing and color options will limit interest in the Flex Capacitor, especially among women and among men with very short or very tall torsos. But due to SD’s newcomer status and to the state of the retail backpack market (i.e. dominated by Osprey, with a few pegs leftover for everyone else), SD believes that a tight assortment is its best hope of gaining a foothold.

2. It’s not “ultralight.”

With relative ease, we could have substantially reduced the weight of the Flex Capacitor, which currently specs at 2.5 pounds (1.1 kg). How? Mostly, by:

  • Eliminating its full suspension, back panel padding, and hipbelt;
  • Removing its six exterior pockets;
  • Using a lighter weight fabric; and,
  • Shrinking its volume, or at least making it static (rather than adjustable).

These actions may have pleased the thru-hiking community, BPL forums, and r/Ultralight, but it would have left the broader market longing for more. Frankly, I’d be looking elsewhere, too. IMHO, the extra 16-24 ounces is well worth the improved load-carrying performance, convenience, durability, and versatility.

3. No rear shove-it pocket, sleeping bag compartment, or tall side pockets

The single most standout feature of the Flex Capacitor is its adjustable volume, using the gusset on its frontside. Unfortunately, this feature is incompatible with a rear shove-it pocket and a sleeping bag compartment.

Oh, well.

Shove-it pockets compromise load-carrying performance (because the weight is far from the user’s center of gravity, and often sits outside the compression system) and are abrasion-prone if made of mesh. When using the Flex Capacitor, I store oft-needed items in exterior pockets or at the top of the main compartment (easily accessible via the zippered top lid); and I store wet items like my rain gear and tent fly inside the main compartment but outside my pack liner.

I struggle to see the case for sleeping bag compartments, and wonder if they are just a relic from a bygone era when sleeping bags were much less compact. When I pull into camp, everything must come out of my pack — shelter, food bag, stove, puffy layers, etc. Why is a second access point supposedly more convenient?

Finally, tall side pockets are not accessible without taking off the backpack. At that point, why store items outside the pack, when they would carry better and be more secure inside the main compartment?

Rear shove-it pockets are conveniently accessible, but they don't carry weight well and they're abrasion-prone when made of mesh.

Rear shove-it pockets are conveniently accessible, but they don’t carry weight well and they’re abrasion-prone when made of mesh.

4. Lack of “wrap”

Frameless backpacks fit like a glove — they conform to the user’s back, not the other way around. Unfortunately, frameless packs cannot comfortably carry loads of 25-ish pounds or more. To carry more weight, you must use a full suspension backpack.

Whether in a frameless or full suspension pack, weight carries best when it is flush against the back, so that it minimally affects the user’s center of gravity. Unfortunately, this direct contact results in SBS, or “sweaty back syndrome,” especially in hot and humid conditions.

To avoid SBS, there must be airflow between the user and the backpack. Unfortunately, this pushes the load backwards and compromises load-carrying.

See the tradeoffs?

The Flex Capacitor is a full suspension backpack with decent airflow around the kidneys. But it does not “wrap” the user like a frameless pack will, and its load-carrying is not at max potential. Further refinements to the back panel pods and hip belt may improve things.

The Flex Capacitor has a stiff Y-shaped internal stay (pulled out for this photo) and a three-pod back panel that provides airflow around the kidneys.

The Flex Capacitor has a stiff Y-shaped internal stay (pulled out for this photo) and a three-pod back panel that provides airflow around the kidneys.

5. Stretch mesh side pockets

The side pockets on early Flex Capacitor prototypes were made of durable pack body fabric. They were easily accessible and could be locked off when bushwhacking. But their bulbousness ruined the pack’s otherwise “clean” look, and the lock-off was clumsy.

The side pockets are now made of stretch mesh. They look much cleaner, and they are still easily accessible — they have some dimension, and are not flush against the pack body. However, they will be more abrasion-prone, even though we’re using the heaviest mesh available, and there is no security feature.

6. Top lid zipper snags and aesthetics

The Flex Capacitor’s main compartment is accessed through a zippered top lid. Getting in or out is refreshingly quick, relative to the sequence of buckles, straps, cords, and roll-tops on most packs.

However, it’s not entirely annoyance-free, as the #10 zipper can snag on the rainguard. We could have eliminated the rainguard by using a watertight zipper. But such zippers are:

  • Expensive
  • Less durable
  • Less easy-gliding
  • Not waterproof in extended wet conditions

Plus, we didn’t want to give the illusion that the pack is waterproof when it is not. To keep dry items in the main compartment, I recommend using a 20-gallon Brute trash compactor bag.

Unless the pack is stuffed full, the top lid will sag and “mushroom.” It’s merely an aesthetic issue, and common among packs with top lids.

When not stuffed full, the top lid will sag and create a "mushroom" look.

When not stuffed full, the top lid will sag and create a “mushroom” look.


Disclosure: This post contains affiliate links, which help to support this website.

31 Responses to Room for improvement: Self-critique of the Flex Capacitor 40-60 Pack

  1. MarkL August 31, 2016 at 11:23 am #

    I like it when a company tries to break out of a design rut and offer something new. This echos some other concepts out there, such as the venerable Wild Things Andanista, but with a broader target customer.

    First a couple questions:
    1: Seasonal versatility: Is the pack body material durable enough to use as a 4-season pack, where you may be strapping snow shoes to the front or sides? You also say no metal edged skis. What is the particular issue with them? The straps or the pack body?
    2: Frame: Since it is a tubular frame I assume the stays can’t be re-shaped to conform to the user as you can with removable flat stays. Are there other ways to “customize” the fit for different body types? Or is the idea that its rigidity actually makes it carry closer to a traditional external frame?
    3: Sizing: You mentioned different sizes and belts. Can you mix an match those at purchase, or will you need to buy the pack and then a different belt as an accessory?

    A few other thoughts:
    1: Thank you for putting out a product that doesn’t cave to the ultra-light fanaticism that seems to be dominating the conversation recently. There is a balance between weight, durability, versatility, comfort, price, etc., and for most people weight is not (or shouldn’t be) the defining issue. This at least looks like an honest attempt to find that balance. So far I feel the same way about the Tarptent I recently purchased. I could have gone lighter, but I would either have had gossamer fabrics, had to give up some comfort/livability space and features, or paid 3 times as much. As it is, I have a very livable shelter (decent space for 2, a palace for one) that is still half the weight of my previous 2-person. This looks like it is born of a similar philosophy.
    2: Re Shove-it pocket: I have old (like 15 years old) Madden Mountaineering packs and the pocket is absolutely part of the compression system. Seems like that is not that unusual in the packs I’ve looked at recently, but I’ll have to look more closely. I mostly use it for flat things like my map case and shovel blade. That being said, this doesn’t seem like a winter-oriented pack, so that may be a reasonable design sacrifice.
    3: Re top pocket: I have always liked a hinged or floating lid. In general I don’t like relying on zippers on a pack, especially in a critical area. I like being able to just tuck a coat (or a sleeping pad, or a climbing rope) under it. If I end up having to carry a partners stuff it is easier to overpack. Just in general it seems like a more versatile design.
    4: I agree that the sleeping back compartment is unnecessary, although I now find myself using the one on my old pack for my bag, pad, rain gear, etc. It’s accessibility actually negates some of what I have traditionally used the shove-it and floating lid for.

    • Andrew Skurka August 31, 2016 at 12:49 pm #

      1. I would feel comfortable with strapping snowshoes to the pack, but I’d be wary of metal-edged skis due to the sharp edges, especially if the pack fabric is sandwiched between the ski and something hard like a stove pot.

      2. No, it cannot be user-adjusted. Retailers and SD team members (notably that of one of the main designers, who was formerly at Osprey) were consistent in their opposition to this. Basically, many more people screw it up than get it right.

      3. The hipbelts will be matched with packs of the same torso length, e.g. medium hipbelts on medium sizes. But SD and retailers will have extra hipbelts available so that you get the right fit. It would make sense if you could order a torso and hipbelt size when you purchase the pack at SD.com, to avoid playing mail tag, but I can’t confirm that.

      • Fowler August 31, 2016 at 10:15 pm #

        #2 strikes a chord, most won’t come out and say it (kudos) but a lot of designing for the public is constraining their opportunities to mess up a product. This is “lowest common denominator” stuff, but it is the reality of business. Cottage companies can get away with much more, but anyone selling retail has to deal with this front and center.

  2. robin August 31, 2016 at 1:36 pm #

    Aside from the obvious unique feature of the adjustable capacity, this bag really only compares two a couple others on the market that I can think of: the ULA Circut, and the Osprey Exos, and the Gossamer Gear Gorilla/Mariposa. I wonder if you might write up a comparison of these products. (I’m sure there are others, but these are very popular packs in same weight/size that feature full suspension). I had narrowed it down to those few packs before yours came out and went with an Exos 48 that I found at a garage sale. It’s been killer all summer – large enough to hold everything I need for a 9 day high sierra trip, and as lightweight as I would want for pack weights between 18-35 lbs. The mesh pockets are showing wear, but other than that it’s been great. Other than the increased capacity and adjustability, what else does your pack have going for it over the Exos, Circut, or Gorilla/Mariposa? (comfort, durability, load carrying, etc?)

    • Andrew Skurka August 31, 2016 at 2:11 pm #

      I can only comment credibly about the Circuit, which I’ve used personally and which I’ve lent to a lot of guided clients. The other comments are speculation.

      In general, the three packs in question will have more size and color options. The Flex Capacitor will be more versatile due to the adjustable volume — it’s like a Circuit/Catalyst, Exos 48/58, and Mariposa/Gorilla in one.

      Versus the Circuit, the Flex’s suspension carries heavier loads better, because it’s stiffer and anchors directly into the hipbelt; the top of the stay is also higher, so more weight can be be released off the shoulders. Cleaner access to the main compartment (vs roll top). Less expensive by about $50. Similar functionality for the hipbelt and side pockets. The ULA packs ride closer and “wrap” better, but have no airflow through the back panel. They have rear shove-it pockets, if you like that feature. The ULA packs are made in the USA, use more premium fabrics, and the owner Chris will pick up the phone if you call.

      The Osprey probably fits better. Suspension is less capable. Side pockets are less accessible. Main compartment access has more steps.

      The Gorilla is much more limited with load-carrying. Its exterior pockets are convenient, but for my purposes I would rather everything be inside the pack, where it carries best and is more secure.

  3. Robin August 31, 2016 at 2:59 pm #

    What do you mean the Osprey fits better? A more fitting comparison, or actually will fit my body better?

    • Andrew Skurka August 31, 2016 at 3:06 pm #

      In general, the Osprey has a more body-sculpted fit. But that’s not to see it will always fit you better. For example, read about Dale’s recent experience with the Exos.

      Backpacks are only one notch below footwear in the finickiness of their fit. YMMV.

  4. David August 31, 2016 at 7:08 pm #

    Andrew, if you want to see the perfect side water bottle pocket in action, have a look at Mchale Packs. They are removable, you can adjust the height of them on the pack, and you can angle them for really easy access to a water bottle or you can have them verticle to carry things you want to stay put.

  5. Shawn K. August 31, 2016 at 8:25 pm #

    Public self-critique? That’s not how you’re supposed to behave! It’s almost like you care about having your name attached to a project. 🙂

    I recently changed packs and I find a two strap hip belt to be more supportive and comfortable, as the top & bottom can be adjusted separately for a custom fit. Better fitment also may reduce the amount of hip belt padding required, which should help offset the weight & cost of the new design.

    It looks like a good balance was struck between pockets/features and weight. Over time, I’ve grown to dislike sleeping bag compartments and other internal organizational efforts. They just get in the way, while adding weight & cost. The same goes for attempts at waterproofing the pack; watertight zippers aren’t worth the bother.

    I look forward to seeing more Skurka Rated™ products from you and SD. In a world full of outdoor stupidity like that awful Tincup Whiskey ad, it’s refreshing.

    • Andrew Skurka August 31, 2016 at 8:31 pm #

      Hadn’t seen that Tincup Whiskey ad before, https://youtu.be/_rUyld6KTi4

      Boy, that may define outdoor stupidity.

      • MarkL August 31, 2016 at 11:51 pm #

        Wow. That’s a high rate of stupid per second.

  6. Rudy September 6, 2016 at 5:09 am #

    Re: “…SD believes that a tight assortment is its best hope of gaining a foothold.”

    That seems counter-intuitive. I would think restricting options such as size and color would have the opposite effect and become deal-breakers for a lot of people (of course, maybe these people aren’t your targeted audience). The “tight assortment” strategy seems more akin to the tact taken by movie studios who are unsure as to whether their new release will be embraced by the public. They release it to a small number of theatres and then wait and see how it performs before deciding their next step.

    Regarding the bag itself, I’m very intrigued. I hope these show up in REI or MEC. I’d love to try one on.

    • Andrew Skurka September 6, 2016 at 7:14 am #

      It was counter-intuitive to me, too, when I was first told about it. But it makes sense: SD’s primary “customer” is a retail buyer, not the person who eventually will use the product.

      After placing orders with their tried-and-true pack brands (i.e. Osprey), this retail buyer has only a few remaining pegs and dollars for packs from other brands. In this context, SD’s two SKU’s is more attractive than three SKU’s (S, M, L) or six SKU’s, (S, M, L in two colors, or a men’s and women’s). They can commit fewer resources to the program while still bringing it all in.

      • Rudy September 6, 2016 at 10:12 am #

        That makes perfect sense. I hadn’t thought of it from that angle. Going up against Osprey must be an uphill climb (pun intended). They have become such a monolith in the industry.

  7. sqidmark September 8, 2016 at 3:14 pm #

    I know I’m splitting hairs here but I believe that in order to address a problem you first have to properly identify it.

    Most folks, including manufactures/marketers, always point to prevention of sweaty backs as the reason for designing pack ventilation. I know that I can hike up Mt Tammany at the Delaware Water Gap without a pack and be just as sweaty as I would be with one. However, I find that I have to use packs with trampoline style suspension in order to prevent heat build up and subsequent irritation from the pack. Of course even with the trampoline I still sweat a great deal, but at least I don’t feel like ripping the pack off and throwing it on the ground after the first mile or two. So, sweat is not so much the problem as is irritation due to heat build up. Engineer from that perspective and perhaps a slightly better solution will come to light.

    I notice that the Flex Capacitor has fairly limited back contact with lots of open space. I’d be curious to see how this feels as it could to be the best alternative to trampolines I’ve seen yet.

    Hands down the most comfortable pack for me is the Atmos, and for my wife the Aura. Although I’m keeping the Atmos, it has a couple of things I don’t care for and besides I wanted something much lighter. I had purchased/returned and otherwise tried out quite a few packs, both trampoline and non. Finally settled on an Arc Haul. It’s not quite as Cadillac comfortable as the Atmos, but I can hike all day with it and it’s a lot lighter. I had it made with a Mariposa style tall left pocket for my hammock tarp, spreader bar etc.

  8. Robin September 9, 2016 at 2:04 am #

    You could solve the “stash it” pocket issue by adding an Exped Flash Pack pocket http://www.exped.com/usa/en/product-category/backpacks/flash-pack-pocket-0

    Perhaps Sierra Designs could make a detachable pocket as an accessory.

    • Andrew Skurka September 11, 2016 at 8:16 am #

      You could, but you will no longer be able to adjust the gusset.

      On Thurs/Fri I wore a pack with a shove-it pocket. It was nice to have, but it was no better than an easy-opening top lid. In fact, I’m tempted to say that shove-it pockets are mostly a byproduct of roll-top closures, which are a relative nuisance to open and close.

      • MarkL September 18, 2016 at 5:05 pm #

        I think it is really an offshoot of the shovel pocket on winter packs.

  9. Jennifer September 18, 2016 at 9:33 am #

    I’m finishing up my first season of backpacking ever at 56 (loving it!) and hike primarily in the California Sierra Nevada, Trinity Alps, areas where bear canisters are required. I tried a few other lightweight backpacks (ULA, Granite Gear) and chose the Exos 58 because it was the only one I could wear without feeling the bear canister uncomfortably against my back. The size small fits my 17″ torso quite well. How does the Flex Capacitor do with a bear canister?

    • Andrew Skurka September 19, 2016 at 8:31 am #

      The Flex Capacitor can fit the BV500 horizontally, but I’d recommend that you keep it vertical.

      Not sure what ULA or GG packs you were using. But in general the Flex Capacitor keeps the load further off the back. In this case, that’s a good thing, because you won’t feel the canister as much. But it’s a tradeoff — for example, most ULA packs feel more snug because they sit closer to the user.

  10. Brad November 28, 2016 at 10:36 am #

    Is there room to carry bear spray just to the rear of the hip belt pocket? It appears that there is a stabilizer strap there that might work. I would rather carry the canister on my hip than in the shoulder strap pocket. In fact, I prefer that packs have a modular design to the hipbelt pockets, but unfortunately that isn’t the direction that most manufacturers have taken. On my Exo Mountain Gear pack, I carry a removable pocket on my left side and bear spray on my right. I am anxious to see the pack up close and personal…looks intriguing.

    • Andrew Skurka November 28, 2016 at 12:56 pm #

      There might be room for a holster in the wedge between the hipbelt pocket and side pocket. Historically, I have carried mine in the side pocket (with nothing else in that pocket, so I don’t grab something else when I REALLY need my spray), but with this pack the shoulder strap pocket is very convenient.

  11. Rodney December 31, 2016 at 4:37 pm #

    Andrew, I’m very interested in this pack. My only issue so far is a sleeping pad. I have the Thermorest zLite and I see only two ways to carry it with this pack…1) Inside, though that would take up considerable room or 2) strap it to the outside. I’ve strapped it to the outside of my previous pack, Osprey Atmos 50, but I feel more secure knowing my pad isn’t secured with a piece of rope or bungee cord. Any suggestions with the Flex???

    • Andrew Skurka December 31, 2016 at 5:08 pm #

      I would first suggest at some point that you upgrade to an air pad. I know they are pricey and less reliable, but the increase in comfort is dramatic. Not sure where you backpack, but my standard summer pad is uninsulated and cost me just $40 deeply discounted, 12 oz or so.

      Now to your question. If I carried a pad on the Flex I would use the two horizonal compression straps. Not ideal but it will be very secure there. There is enough spacing between the end anchors that you could strap it on one side or on the very back. I would not worry about covering the gusset — I set it in the morning based on pack volume and forget about it until tmrw.

  12. Brad January 16, 2017 at 1:02 pm #

    Andrew, I have an 18 1/2″ torso and a 33″ waist. Do you think I would get a better fit if I picked up a Medium while there are still some left, or wait until they make the switch to S/M and M/L sizes? One issue for me is the current packs are excluded from Pro Deals, so I would not get a discount. I have no idea if the future models will be excluded as well.

    Thanks,
    Brad

    • Andrew Skurka January 16, 2017 at 1:16 pm #

      You are right on the cusp. Unless you need a pack now I would wait until the next stock arrives. SD CS will know when that is.

      Another perk: better hip belt than on G1.

      Unsure about pro deals.

      • Brad January 16, 2017 at 1:27 pm #

        Can you elaborate how the hip belt is better? I have heard it will be removable so you can switch sizes, but with my torso and waist size, I usually don’t require different sizing between the two. Are there other improvements?

        • Andrew Skurka January 16, 2017 at 2:53 pm #

          The new hipbelt is interchangeable, but it’s a more ergonomic belt. I’m going over the office later today and will try to remember to get a photo to post here.

        • Andrew Skurka January 17, 2017 at 8:56 am #

          I wrote an entire post for you about the hipbelt and about other changes to expect when this next batch arrives,

          http://andrewskurka.com/2017/flex-capacitor-changes-sizing-hipbelt/

  13. Rodney January 17, 2017 at 12:29 pm #

    Andrew, I just received the pack yesterday and I think I’m going to love it. I am however, a little bummed that a new version is coming out soon. Wish I had seen this a week ago. Do you know if SD will do a swap? Or is it really unnecessary? I’m looking forward to showing off this pack on the PCT this year and will be spreading the word.

    • Andrew Skurka January 17, 2017 at 1:38 pm #

      The new batch of inventory is not a new version, and is not necessarily an improvement. For example, if your torso length is size 19, currently you are a perfect Medium. But with the new stock you will be borderline between S/M and M/L.

      As for the hipbelt, the new ones are slightly more designed, but the current one is perfectly capable. Nearly all of my experience with the Flex (e.g. testing protos, carrying out an elk) was with the current single-layer hipbelt, and I was happy with it. If you’re happy with it, too, I would run with it — the new version might fit you as well.

      No other changes were made to the pack.

      We’d love to hear how the pack holds up on the PCT. Let us know afterwards.

Leave a Reply

Please prove you\'re not spam: * Time limit is exhausted. Please reload CAPTCHA.