The ZPacks.com Arc Blast Backpack is an ultralight cuben fiber backpack with an external carbon fiber frame that is available in three sizes: 45L, 52L, and 60L. Weighing just 17.4 ounces in the 60L version (shown here in orange), the Arc Blast is rated for 30 pound loads making it ideal backpack for thru-hikers and lightweight backpacking trips with up to a week’s worth of food.
If you’re not familiar with cuben fiber, here’s a fast primer. Cuben fiber is an ultralight material used by several ultralight backpacking manufacturers that is lighter weight and more rip resistant than conventional tent and backpack fabrics. For example, if a 2 pound tent or backpack made using silnylon or dyneema grid weighs 2 pounds, it will weigh approximately half that or 1 pound when made with cuben fiber.
More technically, cuben fiber is a non-woven, laminate fabric made using ultra-high-weight-molecular polyethylene and polyester that produces an exceptionally strong and waterproof material. It’s also considerably more expensive because production is controlled by one company that makes it in small batches and because gear manufacturers have had to evolve manual fabrication and styling processes (glueing and taping as opposed to sewing) to create products using it. That price is unlikely to go down because cuben fiber products are too expensive to produce in large quantities.
The Arc Blast backpack reviewed here is constructed from 2.92 oz/sq yd cuben hybrid fabric. This material is cuben fiber on the inside with a protective layer of 50 denier polyester on the outside. The outer layer gives it even more strength, prevents fraying, and makes it possible to dye in different colors.
ZPacks.com has been making cuben fiber backpacks and tents for eight years and has built the highest volume manufacturing capacity (all USA-based) for creating ultralight backpacking tents, backpacks, clothing, and accessories using the material.
Internal Storage and Organization
The ZPacks Arc Blast Ultralight Backpack is configured as an ultralight backpack with a front mesh pocket and two side water bottle pockets, so you can keep most of the gear and food you need to access during the day on the outside of the pack without having to open the main compartment.
The front mesh pocket is fairly small compared to other ultralight backpacks and does not stretch which can make it difficult to fit rigid objects such as a wood stove or cook pot into it. On the flip side, the mesh weave is fairly wide, making it easy to see the contents of the pocket, although I wouldn’t trust its durability for off-trail use.
The side bottle pockets are sized to hold 1 liter soda or Nalgene bottles, which are reachable when wearing the pack, and have drain holes sewn into the bottom. They’re a tight fit however, when the pack bag is full, making it difficult to add tent poles or other gear to the pocket when a water bottle is carried.
The top of the pack closes with a roll top, dry-bag style closure that has a velcro strip to ensure the pack bag top is closed before you roll it shut. However, the end clips of the roll top only close on top of the pack and not along the sides, which can be awkward and catch if you’re hiking through overhanging vegetation.
The inside of the pack bag is cavernous in the 60L size and can really hold a lot of gear or food. The interior is also fully seam taped to prevent water from leaking into the pack when it rains or the pack is set on wet ground. The only openings into the main pack bag are dual hydration ports (there’s a reservoir hang loop inside the pack), which are located between your shoulder blades at the top of the frame.
When packing the Arc Blast, I’d advise you to keep as much of your gear as loose as possible if you need to maximize your volume utilization to carry a lot of gear or food, rather than packing it in a lot of stuff sacks. The hybrid cuben fiber fabric used in the pack has very little “bend” in it and won’t wrap itself around bulges created by stuff sacks. If you must use stuff sacks, use ones that have drawstring tops that can vent excess air when stuffed. The pack bag on the Arc Blast is sufficiently seam-taped and water-resistant that you don’t need to use (so-called) waterproof stuff sacks when packing it.
External Attachment Points and Compression System
The Arc Blast provides an impressive array of options for attaching external gear to the outside of the pack. Many of these attachment points can also be used to add accessory pockets sold by the manufacturer, third party products such as external camera pockets, or trip-specific cordage solutions you whip up on the fly to carry bulky gear.
First off, the Arc Blast shoulder straps and hip belt have daisy chains sewn across them. They’re a little crude looking but it’s easy to add pockets using quick-attach tri-glide buckles or cord.
The pack also comes with a fairly unique way of attaching a foam pad to the outside of the pack (shown above) that includes two cords attached at the base of the mesh pocket and the bottom of the pack, than are tightened using line loc adjusters. Despite marketing perceptions, most triple crown thru-hikers still carry foam pads because they’re far more durable than air mattresses, and this attachment point is a great place to carry a foam pad like this, out-of-the-way.
The Arc Blast has gear loops sewn to the sides of the pack and comes with a non-elastic cord arranged in a zig-zag pattern that can be used for compression or to secure gear to the side of the pack. In practice, I find that this strap geometry makes it difficult to secure or release bulky gear like snowshoes to/from a pack, but there’s nothing to prevent you from removing it or adding additional cord/cord locks to create a more “horizontal” compression/external attachment. You can also run cords over the front mesh pocket to secure other bulky items to the outside of the pack.
Backpack Frame and Suspension
The Arc Blast is an external frame backpack with a lightweight carbon fiber that frame serves several functions.
- The frame helps keep the torso length and fit of the pack the same, no matter how much weight you carry in the pack. This makes the pack easier to use for transitional lightweight backpackers who are less familiar with the nuances of fitting and loading ultralight backpacks.
- The frame suspends a ventilated back panel that makes the pack more comfortable to wear in warmer weather, in part because your shirt will dry faster when you sweat.
- When adjusted, the external frame creates a curve that concentrates the load onto the back of your hips regardless of your waist size, allowing you to hike with a more upright and biomechanically efficient stance.
The effect of the curved external frame is further enhanced by the fact that the hip belt is sewn to the back of the pack, unlike backpacks where it’s less securely attached using velcro. A sewn attachment always trumps a floating one, providing a more continuous kinetic chain, so that pack moves when your hips move without any wasted or diffused energy.
To created the curvature, ZPacks recommends adjusting the frame so that the mesh panel is 2.5 inches off the back of the pack. This adjustment is made by pulling forcefully down on the line-loc cords that suspend the mesh panel. Unfortunately, these line-loc cords slipped repeatedly when I wore the Arc Blast, but this is easily remedied by tying a simple overhand knot in the cord so it can’t slip through the line-loc channel. If there’s an upside to the use of line-locs in many places on this pack, it’s that they make user customization and adjustments possible.
Whenever I test backpacks that are available with custom or add-on options, I make a point to obtain the base pack from a manufacturer to see if the vanilla model is fully functional for its intended use. This proved to be the case with the Arc Blast base model.
If you can afford to customize the pack or add a few options to it (most don’t require any sewn modification and attach using cords), there are a few that I would recommend to make the pack more convenient to use and bring it to complete parity with competitive products.
Adjustable torso w/ load lifter straps attached to frame ($8): Fit can be tricky with this pack because tensioning the external ventilated frame makes the pack noticeably shorter. Furthermore, ZPacks uses an unconventional heuristic of sizing backpacks based on an individual’s height rather than torso length, so that having an adjustable frame will ensure that you can dial in the fit of the pack to your exact physical measurements. The adjustable frame also connects the load lifter straps to the frame instead of the pack bag, making them more effective.
Belt pouches (41.95/pair): Hip belt pockets eliminate the need to open your pack frequently if you carry a lot of little things like Aqua Mira Bottles, bug dope, lip balm, food bars, sunglasses, hair ties, etc. If you’ve ever owned a pack with them, you’ll understand.
Top side pockets ($35/pair): These are pockets that can be attached to the side of the pack, at about shoulder height. They’re indispensable for storing wet or smelly items like a wood burning/solid fuel stove and cook pot ,which you don’t want to put into the main compartment of the pack, and which may be too big to fit into the front mesh pocket.
Lumbar pad ($12): Helps improve load transfer of frame to your hips if you have a flat ass or square hips.
The Zpacks Arc Blast Ultralight Backpack is optimally configured for multi-day backpacking trips and three-season thru-hikes with many innovative features including a ventilated external carbon fiber frame and seam-taped cuben fiber construction. Weighing just 17.4 ounces in the 60L size, it’s a deceptively sophisticated backpack that works extremely well in its base configuration but can also be enhanced using add-on accessories sold by the manufacturer or third-parties. While not as polished looking as other ultralight backpacks made using more conventional fabrics, the Arc Blast 60L is a durably constructed, feature rich, and easy to customize pack making it a very attractive option for backpackers who want to slash their gear weight without sacrificing on comfort or fit.
- Shoulder pads are free to rotate around different chest shapes
- Side water bottle pockets are reachable while wearing the pack
- Side water bottle pockets are solid panels with drain holes and more durable than mesh ones
- Compression and external attachment system can be customized using gear loops located around perimeter of pack
- Pack add-ons can be added any time after purchase and be trip-specific
- Pack is nearly waterproof with seam taped seams (except for hydration ports)
- Orange color is rad. I love it!
- Roll top closure does not secure along sides of pack, only on top
- Front mesh pocket is not stretchable and quite limited in size
- Non-standard sizing system
Disclosure: Philip Werner (SectionHiker.com) received a loaner Arc Blast backpack from ZPacks.com for this review.
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Written 2015.Editor's note: Help support this site by making your next gear purchase through one of the links above. Click a link, buy what you need, and the seller will contribute a portion of the purchase price to support SectionHiker's unsponsored gear reviews, articles, and hiking guides.
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