Ultimate Direction Fastpack 20 Review

First things first, if you know Ultimate Direction, you know them as hydration-pack and hydration-accessory makers. The Ultimate Direction Fastpack 20 ($149.95) is decidedly not *just* a hydration pack. It’s a pack meant for carrying a boatload of water, sure, but also fuel, gear, and whatever makes your heart content for a verrrrry long day of running or multiple days of ultralight backpacking/fastpacking. Second, the following review is a bit obsessive. I’m not sorry about that, though! This review is a result of at least 100 hours of testing on long day hikes and runs as well as a five-day fastpacking trip. Let’s do this.

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The Ultimate Direction Fastpack 20 in action. Photo: iRunFar/Bryon Powell

General Information

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The Ultimate Direction Fastpack 20. All photos iRunFar/Meghan Hicks unless otherwise noted.

The Fastpack is advertised at 1 pound, 3 ounces/535 grams. My size small/medium, which was a pre-production model, weighed 552 grams on my scale.

The pack comes in two sizes, small/medium and medium/large, based upon chest measurements. My chest is squarely in the middle of the small/medium size’s measurements, yet with both of the chest straps cinched all the way down, I could get the side straps within about 1.5 inches of being fully cinched, and this is with the pack totally full. I’m not sure what someone with a super-tiny rib cage would do here.

The pack is advertised at 20 liters–absolutely no way. It’s liters bigger than this. I’m guessing you can top out the main compartment at 25-ish liters and still get it to shut. And then you have the mesh back pocket in which you can almost store the world. Easily a 28-ish-liter pack before you start adding in the side and chest pockets.

Unlike some ultralight packs I’ve used, there’s not yet a maximum recommended carrying load. Buzz Burrell told me he’d tested at up to 18 pounds. I’ve worn the pack at everything from eight to 20 pounds. The pack is super comfy as long as it’s packed well at any of those tested weights, and I can hike no problem at these weights, too. For me, however, I can’t actually run at weights above 14 or 15 pounds, as I get to much side-to-side swing across my rib cage. More on that soon.

Pocket Configuration

Main compartment

This is basically a modified cylinder with a roll-top closure. The closure has two Velcro pieces and is firm like the top of a dry bag so you get a good seal when you roll. You then secure the top with two side straps that, when tightened down, will secure/cinch not only the top but the sides of the bag. A super-snug fit is what you get around whatever is in your pack with tightening these two straps; simplicity and functionality perfected here. The main compartment is water resistant, and I’ve found it will keep things dry in some rain. Of note, the main compartment also does a good job of holding in moisture, such as that of a wet tarp or damp sleeping bag.

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View of a side pocket on the main compartment, a side compression strap that attaches to the roll-down closure of the main compartment, and a side adjustment strap.

Outer mesh pocket on main compartment

This is located on the back of the pack. It’s enormous and super stretchy, but the stretch is firm so you can put something heavy in there and it won’t bounce. This pocket excels at holding bulk, layers you’re shedding and donning all day, a wet tarp or sleeping bag you’re trying to dry out, or extra food. The sky is really the limit with this pocket.

Side pockets on main compartment

Again a stretchy mesh that can hold a variety of objects like folded trekking poles (with the help of the elastic cords on the back of the pack), up to a 1.5-liter hard-sided water bottle as long as you choose a bottle with a smaller diameter, softflasks and collapsible reservoirs up to 1.5 liters, an extra shirt, or hat and gloves. Another highly functional set of pockets, props to the Ultimate Direction designers on these!

Left chest tall pocket

Wide and deep, stretchy mesh, and with an elastic-cord closure. Holds UD bottles or a 500-milliliter softflask very well. Holds hundreds of calories of food. A perfect map holder if you don’t mind tightly folded maps. Nice camera or phone holder. Or a map and camera holder as has worked really well for me. Or a phone and several hundred calories, which also worked really well.

Lower left chest pocket

A small pocket that closes with a zipper and packs some serious punch. Maxes out in holding about 600 calories of bars or gels which is perfect for several hours before having to stop, take off your pack, and resupply from the main compartment. Beware, this pocket gets really sweaty!

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View of the four chest pockets. Photo: iRunFar/Meghan Hicks

Right chest tall pocket

Wide and deep, stretchy mesh, no closure but the diameter of the pocket can be increased or decreased with a vertical zipper. Unzipped, the pocket holds a UD water bottle or a full 500mL softflask. I struggled with carrying a less-than-full 500mL softflask, however. With the pocket zipped, the top of the softflask kept popping out and flapping around. Unzipped and there was too much room for a half-full flask to bounce around. If anyone solves this dilemma, I’m all ears. I stored a UD bottle here with the pocket unzipped for days perfectly, running, hiking, and scrambling/light climbing, and it never popped out or bounced.

There’s a small, stretchy pocket located on the outside of this pocket as well. It’s perfect for salt tabs, your garbage, a bit of toilet paper, a few gels, or a pair of lightweight gloves.

Lower right chest pocket

Another small pocket that, this time, employs a Velcro closure. More food storage? For me it perfectly fits a compass (yep, I’m old school!) and my little baggie of Nuun and salt tabs. Alternately, it fits a set of AquaMira bottles. I never had an issue with the Velcro opening itself, even while scratching over rocks and through downed trees during off-trail use. A secure pocket, for sure. This pocket gets sweaty, too!

Small side pocket on main compartment

A small pocket with a zipper opening. Contains a key holder. Is big enough to hold your credit cards, a headlamp, a passport, or a phone. A stellar pocket for holding the things you desperately don’t want to lose.

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A view of the pocket on the side of the main compartment, including the key holder.

Strap Configuration and Use

Two chest straps

This has been the feature most noted and questioned by the trail ultra community in looking at images of the pack on social media or samples in real life. I agree that it’s very interesting that UD has chosen this route as opposed to one chest strap and something resembling a waist strap. For my body type, at least, the two-chest-strap setup is the pack’s limiting factor. I get the premise, keep the pack as close to running-vest style as possible since that’s such a ridiculously comfortable layout, as we’ve all learned since the concept came mainstream in our niche sport. Also, this design certainly saves weight.

But for me, as I previously mentioned, I can’t run a normal fastpacking running pace (which ranges for me from about four to six miles per hour) with more than about 15 pounds in the pack. I get too much side-to-side movement with more weight than that. This options the pack into a very specific category: for use when you want to go super light. For overnight use, you’ve got to truly enter the ultralight category with the weight of your kit to keep your pack’s weight at something runnable.

A big plus to these straps, they are located on an adjustable track that allows you to find the right height for your body type. For me to get the most supportive fit, I put the top strap as high as it goes and the bottom strap as low as it goes. In doing so, the bottom strap crosses beneath my rib cage, but not quite at the smallest part of my waist. I found this gave the pack the most stability for running, as close to a waist strap as I can conjure with the pack.

I had no problems with the straps sliding themselves on their adjustable track; they stay right where you want them.

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The chest pockets and straps in action. Photo: iRunFar/Bryon Powell

Two side adjustment straps

These straps connect the main compartment of the pack to the front of the pack’s vest, for lack of a better descriptor. They are adjustable and crucial for getting the proper pack fit. There’s not too much to say about these straps. They just do the job they are intended to do!

Pack Accessories

Elastic cord and webbing on the back of the main compartment, and small webbing loops on the bottom of the main compartment

These features are intended to help you lash stuff to the outside of your pack. The most common use of the elastic cord on the top would be to, in conjunction with one or both of the side pockets, attach folded trekking poles. For instance, I tucked my two folded Black Diamond Ultra Distance Trekking Poles into one of the side pockets and used one of the elastic cords to secure their tops. In doing so, I had no problems with bouncing, noise, friction with the pack, or dropping my poles while hiking and running. As is standard with ultralight packs, you have to take the pack off to attach the poles. Also, I have no idea how you’d safely attach poles that don’t collapse/fold.

The elastic cord and webbing on the back of the main compartment can be used to carry ice axes.

Using the webbing on the back and the bottom of the main compartment of the pack, you can attach a sleeping bag, sleeping pad, or other gear using a bit of additional cord/webbing.

Two ‘daisy chains’ on the main compartment

The daisy chains, along with a little added webbing or cord provided by the user can be used to strap lots of interesting things to the back of the pack. Think snowshoes, a climbing helmet, a sleeping pad, or the like. I strapped a bunch of things on as tests, and this functioned fine. Word of advice, whatever you’re lashing on, attach it as firmly as possible to eliminate bounce which is annoying when you’re trying to run.

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View looking into the main compartment showing the inner hydration sleeve, the Velcro strap for securing the bladder, and the sleeve holding the removable back pad.

Inner hydration sleeve in main compartment and other hydration accessories

You can put in up to a three-liter hydration bladder in the internal hydration sleeve. There’s a Velcro tab at the top of the sleeve to which you attach the top of the hydration bladder to suspend it in the right spot on your back. There’s also a tube opening in the main compartment of the pack at the nape of neck as it’s worn, and elastic straps on each shoulder for holding the rest of the tube at the ready for drinking. Let me be frank, I didn’t care for the hydration bladder set up in this pack at all. If the pack is full of gear, you have to empty a lot of it to access the hydration bladder for water refills. To be fair to UD, I have this opinion of almost all hydration packs in which the inner hydration sleeve is directly adjacent to the pack’s storage space. For me, hassle-free access is crucial to actual use. Otherwise, the gram-shaving scissors come out.

Removable back/sleeping pad in main compartment

Big ups to UD for this feature, though I suspect it will only be enjoyed to its full capacity by the ultralight geeks out there. The back pad is removable from a sleeve in the main compartment of the pack. You can thus take it out to sit or sleep on when you’re not using the pack! Again, this is impossible to do if you pack is full without yard sale-ing the contents of your pack trailside for access. The pad is tiny, however; it’s just a piece of padding for your hips that you stuff into your sleeping bag, or enough covering for your sit bones if you wish for a padded seat. For those who are used to this type of ultralight sleeping or chilling, big bonus here.

The back padding is quite spongy but it’s not robust enough to pad your back from something inside the pack that’s on the poke-y side of things. For instance, I tested the pack with a bear food storage can (more on that below), and I had to pad very carefully where the bottom of the canister inside the pack met my back, as the back padding itself didn’t come close to doing the trick.

Another pro tip, you can remove the back padding if you don’t plan to sleep on any pad at all, and stuff other things into the sleeve in lieu of it. A sleeping bag or some clothing provide as comfortable a back pad as the pad itself. This is a fine way of shaving some more weight from the already svelte Fastpack.

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The back pad and its sleeve.

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The back pad removed.

Main compartment handle

Why oh why do ultralight packs come with these? Almost all of them do and they are waste of a little bit of weight. They are the first thing I cut off when I get a new ultralight pack. There are plenty of ways to safely grab or hang onto your pack, like the shoulder straps or by the whole pack itself.

Other notes for obsessives

  • The Fastpack fits a bear food storage can! I tested the pack with the BearVault BV500 and the BearVault BV450 Solo Food Containers. These cans are 8.7 inches in diameter and they slide right into the pack. The pack’s base tapers a bit to a diameter that must be about a half inch smaller than the can’s maximum diameter. As a result, it doesn’t sit 100% flush with the base of the pack. You can get around this by putting something small and mushy (clothing is probably the best choice), to create a ‘platform’ on which the can sits. The other thing you have to do if you want to truly run with a bear can or anything super firm inside the pack (as noted above) is to pad the heck out of the back panel. The back panel, like all ultralight packs, is pretty minimal and this works just fine as long as you consciously don’t pack hard things against it. If you’re going to carry a bear can, use your sleeping bag (loose, not in a stuff sack) or basically all of the clothing you’ve brought with you between the can and the back panel of the pack. Notably, if you’re in the ultralight fastpacking category, you can carry the solo can and your gear for up to four days of fastpacking. If you carry the full-size can made by BearVault or other companies, you better be hiking with a partner who can carry some of your volume because the can basically fills the pack’s main compartment. (This concept works. We tested it for a five-day trip with two people.)
  • Cut the straps to your size and save grams! You’re going ultralight, right? Every gram counts.
  • A solid, comfy, all-day, multi-day fit for ultralight fastpacking packs, for a pack that has been sized to its user properly, is all about how well it’s loaded by that user. Unlike standard multi-day backpacks with an internal frame that’ll hold whatever you carry in whatever helter-skelter fashion you load it, you have to be really careful about how you load the Fastpack or any other ultralight pack. First, think about how to get the back panel to lay soft and flush against your back. Something soft should be there for extra padding and to help the pack ever so slightly contour to the curves of your back. This is critical if you want to run with this pack. If it’s not laying flush against and snug on your back, you won’t be able to comfortably run. Next, think about weight distribution. Get the heaviest stuff to the bottom of your pack to get it to ride low and close to your personal center of gravity. This is key, too, if you’re going to be running. If you have something heavy high up, it will encourage the pack to sway as you run. And it’s going to put unnecessary strain on your shoulders. Finally, save the light bulk for the top of the pack and for that outer mesh back panel.
  • Durability? The materials are more durable than you’ll find on many ultralight packs. Even so, you can’t just go tossing the pack or scraping it around rocks or lifting/lowering it against rocks while you’re scrambling/climbing. That’ll be the fast track to ripping up your Fastpack. Instead, operate with a little care and delicacy and your pack will last a long time. The time I’ve put into the pack so far has yielded no durability issues.

Overall Impression

The Ultimate Direction Fastpack 20 is a bang-up pack. It’s perfect for long day runs and hikes, as well as ultralight overnight trips. The pack has some quirks that, my guess, will be ironed out by the second edition at the very latest. But, it does what it’s supposed to do, and it does that well. Bring on more gear from Ultimate Direction!

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The Fastpack at sunrise in Utah’s Uinta Mountains. Photo: iRunFar/Bryon Powell

Call for Comments

  • Have you gotten your hands on the Ultimate Direction Fastpack 20 yet? Or have you seen it in action? What was your first impression? What do you think of the pack?
Meghan Hicks

is iRunFar.com's Managing Editor and the author of 'Where the Road Ends: A Guide to Trail Running.' The converted road runner finished her first trail ultramarathon in 2006 and loves using running to visit the world's wildest places.

There are 24 comments

  1. @UltraMorgan

    Meghan, I'm using softflasks in the front pockets of a first generation Salomon 12 set. They weren't designed to go together. The fabric of the pocket ends about two thirds of the way up the flask. The only way I can keep the flasks from folding over as I drink from them is to blow air into them to give them "some" rigidity.

    Any idea when this fine piece of kit will make it across the pond? No sign via a quick check on the usual UD retailers.

    1. Meghan Hicks


      Ah! This is a good idea, blowing air back into a half-drunk softflask to get them to stay put in the Fastpack\’s front pockets. Yes, I think this might could work. Thanks for the suggestion!

      1. @UltraMorgan


        One other tip. I find that expelling the excess air before you start drinking is beneficial, otherwise you get a slug of air immediately before the liquid.

        Sound complicated, but becomes automatic after a while, especially when you have expelled a number of valuable mouthfuls of liquid while coughing.


  2. Hoosier70

    Given your experience fast packing, how would you compare this to <insert other favorite packs>? What is better or worse with this design? Thanks

    1. Meghan Hicks


      This is a tough question! By far my favorite fastpacking packs have been the Inov-8 RacePro and RaceElite series, two generations ago. They used to have a RacePro 24-liter model that was fantastic for three or four days of fastpacking. The packs were simple, ultralight–very much like this UD Fastpack 20–but had a waist belt so you could carry a bit more weight. (I can’t wear their current models. They made some big changes to the fit of their packs and they presently don’t work at all for me. I hope they readjust their fitting to fit me back into them!)

  3. RyanRSingh

    Great review. Weird question but how do you think the pack would hold up carrying books/laptop (back to school and plan to run back and forth to class, 12 mi round trip)? I am currently looking at the camelback hawg nv. Thanks so much!

    1. Meghan Hicks


      I think it would work! You could use the back-pad sleeve or the hydration sleeve for your laptop or a couple books, to help secure the heavy items in a place that won’t bounce around. If that doesn’t work, you’d just have to carefully pack the pack so there’s no bouncing of your heavy stuff. I can’t compare to the Camelback Hawg, sorry, as I haven’t seen that one in action.

  4. BuzzBurrell

    "…the following review is a bit obsessive…" We wouldn't have expected anything less! :-) 100 hours in the mountains really showed – great job on the review.

    Your careful description of how to load the Fastpack showed your experience – as with all lightweight gear, how the user uses the gear for their situation is indeed key. For example, for an overnight my method is to remove our nice backpad, and instead wrap my foam pad around the inside of the pack, stuffing everything "inside" it, thus forming a structure. I loathe reservoirs for backcountry, so I use Platypus bottles for extra water capacity, which are really light and easy to fill and clean. Options, options; we're all different.

    The FP20 was very intentionally designed to be adaptable by the user, as adaptation is a key indicator of sustainability. The prototype was first tested by Jared Campbell and I on an all day 5th class new route in Zion NP – then I used the same pack flying home as my airline carryon bag – then it was my commuter bag biking to work the next day. All good. All individual choices.

  5. stuart gates

    Meghan, as you have completed in the MDS event, would you recommend this pack for similar 5D multi-day stage events ? The pack looks like it ticks all the correct boxes.

    1. Meghan Hicks


      Unfortunately, I can’t recommend the Fastpack 20 for multi-day stage racing like MdS, at least for me. This is too bad as, like you, I think it ticks most of the boxes of a pack right for that type of race. When I start MdS, my pack weighs about 18 pounds. That’s all of my gear/food/etc., plus 1.5 liters of water. And I run somewhere between 4.5 and 7.5 miles per hour depending on terrain over the course of each MdS stage. The combination of the running speed plus the weight of the pack would create, for me, too much side-to-side swaying of the pack across my rib cage. In my testing, I realized I could tolerate only up to about 15 pounds before the swaying got to be too much.

      That said, as I would recommend to anyone thinking of multi-day stage racing, get a couple packs, test them, and figure out what’s right for you. Perhaps the Fastpack would work for someone with a different-shaped rib cage or similar?

  6. Tim

    Hello Meghan – do you think they need to do a better job with the sizing and going with Small, Medium and Large? You stated you are inbetween but would you have preferred a smaller fitting pack? I am assuming you had your puffy jacket on most of the time? What if you did not have a jacket on would it have been too big?


  7. measinb

    I just ran around the Wonderland Trail with a Sixmoon Designs Flight 30 (https://www.sixmoondesigns.com/products/flight-30). I did not experience any of the lateral swing that you mentioned with the UD 20 and I was around 20 lbs w/ food for 3 days and up to 2 liters of water. Overall the pack worked well for me.

    I'll be curious to check out the UD 20 when it is available locally as some of the features sound really nice. Good to hear that is in fact larger than 20 L.

    Thanks for the thorough review…never apologize for information! It is always appreciated.

  8. nrkuhl

    Surprisingly breathable. Although my points of reference for this (other similarly sized and used packs I own) are a Hypelite Mountain Gear pack that doesn't even breathe slightly, and the Mountain Hardwear Summit Rocket 20, which just absorbs all your sweat and passes it along to the contents of the pack.

    My Fastpack came in the mail yesterday, and I've only used it so far to commute to school, so these are only initial impressions, but I'm really stoked about the pack. The compression/roll top closure system is really well designed and effective, I think this is the first z-shaped compression system I've ever seen actually work well. Vest straps are very comfortable and fit well for me (5'9" and broad shouldered).

    I really appreciate the adaptability and plethora of storage options – the pack is my new commuting pack, all day running pack and alpine/long rock route summit pack, so it'll be put to the test. For that same reason, I'm a fan of the carry handle – minimal weight addition gives me a super convenient way to hang the pack off a climbing anchor. I do wonder if the sternum straps will be long enough to fit over layers in the winter though.

    1. Meghan Hicks


      I wore the Ultimate Direction SJ Ultra Vest for the Tor des Géants. I was really happy with this pack for the race, plenty of volume for all the required gear, water, and fuel. For me the UD Fastpack 20 would have been too big for the Tor, too much volume. There were people carrying larger packs, choosing to carry more volume than I did. For people looking to carry more gear at the Tor, the Fastpack 20 would be a great option, though!

  9. ertauda

    Any tips on getting a BearVault into the main compartment? It seems like th opening is just a centimeter or two too small. Any advice? Help?

  10. Michael

    Hi, I am thinking to get the UD Fastback 20 for MDS. Do you think this pack can work well in this race? Also, do you think you could carry 750ml bottles (I have raidlight bottles), or will they be too big?
    Have you tried the official MDS pack (pricy!!), if so how would you compare this?

    1. Adam Jones

      Hi. I did the MdS with this pack last year – as did Elizabet Barnes, who won the race. It’s a really durable bag and on the light side as well. The side swing is a definite factor, but you learn to adapt. You need to pack well to make sure everything is easily reached, or you can waste time rummaging. It takes 750ml bottles just fine. Not a great deal of extra storage, and you’ll need to rig something to carry your sleeping bag or mat, but there will be room by end of day three to stuff it in. Biggest negative is probably the packing. Plenty of room on the chest to ensure your race number is visible. Slot the straps behind the bib. The raidlight bags are, unfortunately, not a good choice. The chest straps obstruct the bib and you can get penalised on time, as my brother found.

  11. Jessica Tang

    Like Ertauda above, I can’t fit the bearvault BV450 into the bag through the top opening into the main compartment. It’s about 1-2 inches too small…anyone else having this problem?

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