There are two problems with the SuperUltraLight ethic.
The first is that it motivates SUL aficionados to develop throwaway gear that may last a season, if you’re lucky. I once used a tarp made of an extremely light Cubic Tech fabric (CT0.3.K08, at 11.4 gsm) that blew up in one unfortunate midsummer wind gust in the shadows of the Tetons, while camping at the uppermost campsite near the treeline in the North Fork of Cascade Canyon. And my every attempt to manufacture, take care of, and otherwise use so-called "SUL" packs (including spinnaker versions of the Mountain Laurel Designs Prophet and Gossamer Gear Uberlite G6) made with lightweight spinnaker nylons, polyesters, and Cuben Fibers, has resulted in failure of the fabrics at the seams caused by repetitive stress.
I think SUL gear such as this can serve specialized purposes for the casual hiker, for the hiker who might not care about disposing (and replacing) gear on a regular basis, or for the hiker interested in saving every gram of weight possible for a single expedition (e.g., Andrew Skurka used an ultralight Cubic Tech tarp on his Great Western Loop trek, and I used a Cuben Tech pyramid shelter for the Arctic 1000).
The second problem with the SUL ethic is that it motivates people to apparent insanity, by which every possible bit of function and durability is sacrified for the sake of meeting a weight spec. I’m speaking a bit tongue in cheek about this insanity of course, since I seem to be a regular participant and proponent of it, but I do increasingly value that elusive and ill-defined metric we call the "performance-to-weight ratio".
That’s why I was pretty excited when I took my new ZPacks Blast 18 backpack – a heavy duty Cubic Tech weekend pack that weighs a scant 3.3 oz – out of its mailing envelope…
Joe Valesko, the designer of the Blast series and the owner of ZPacks, made a prototype out of the same fabric (CTK5.18). He put it to good use, completing the 2,600-mile Pacific Crest Trail with it in 2007.
At less than four ounces and roomy enough for a weekend of SUL gear (30L), the ZPacks Blast 18 certainly qualifies as "SUL" by the standard set several years ago by the Gossamer Gear G6, but is far more durable (yet has a similar weight as the first G6).
So, what might differentiate the Blast 18 from other SUL packs is its durability. Instead of the sub-30 gsm Cubic Tech variants found among manufacturers promoting SUL tarps, stuff sacks, and other gear, the Blast 18 uses Cuben Fiber 5K.18, a 48.4 gsm fabric with a stiff hand that gives the pack robust shape, waterproofness, and outstanding durability in both seam strength and abrasion resistance.
About the Fabric
The primary problem with the use of Cuben Fiber in outdoor gear is its seam strength. The fabric is better characterized as a plastic film reinforced by a low-density fiber matrix than conventional woven outdoor gear fabrics, which are typically high density wovens reinforced by waterproof coatings and/or calendaring.
Cubic Tech CT5K.18 is far more durable than its ultralight cousins (e.g., the model CT2K variants) primarily because of its weight, film thickness, and higher fiber density than CT2K.08.
The bottom line is that CT5K.18 has good tear strength (190 lb/in, vs. 105 lb/in for CT2K.08). And, while I don’t have data for seam strength or abrasion resistance, my field testing and inspection of seams under load indicates that CT5K.18 may actually be suitable for long term use and thru-hiking. Don’t expect a miracle, however: this fabric is still considered ultralight and won’t perform to the strength standards of most heavier woven fabrics. Seams will fail over time if you consistently pack heavy loads in a pack like this (I found seams starting to separate in response to the all-day stress of hiking with 35-lb loads), and the fabric is more subject to punctures from sharp things (e.g., thorns and deadfall), more so than woven nylons such as the 210 Dyneema grid ripstops that have been popular in packs by ULA and others.
|1800 cu. in.|
|3.3 oz (Base Model)|
|$105 (Base Model)|
|Cubic Tech CT5K.18|
Shoulder Strap Padding:
|1/4" Closed Cell Foam|
- Nonelastic drawcord top closure
- Two side water bottle pockets with elastic closure
- Large rear pocket with elastic closure integrated with top side drawcords for compression and securing gear
- Frameless design, no back padding or other structure
- Padded shoulder straps
- Optional build-to-order features are available for extra cost and weight. For example, a full featured pack containing a padded wing belt with belt pouches (1.9 oz, $39), sternum strap (0.3 oz, $6), shoulder strap daisy chains (0.2 oz, $8), hydration port ($4), hydration sleeve (0.3 oz, $10), outside shock cord loops that could secure a sleeping pad or tent horizontally (0.4 oz, $7), shock cord compression system (0.4 oz, $9), top strap (0.4 oz, $9), haul loop (0.4 oz, $2), one ice axe loop (0.1 oz, $4), sleeping pad sleeves (0.5 oz, $20), two shoulder pouches (0.6 oz, $28) would come to a weight of 8.8 oz and cost $251.
My favorite "I can’t believe I didn’t think of that" feature of the Blast 18 is the circumferential compression cord that serves three functions: a strap for securing tall gear extending from the pockets (such as trekking poles), load compression for the upper part of the pack, and the elastic closure for the top of the back pocket.
Load Carrying Capacity
The base model of the Blast 18 does not include a hip belt, has a narrow profile, and rides high on your back (the nature of most small packs). This creates a bit of bob and wobble, but padded shoulder straps, the narrow design, and high center of gravity makes "heavier" loads (less than 15 lbs) more comfortable than belt-less packs that are fat and short, and ride low.
Assessing the load carrying capacity of a frameless pack, especially one without a waist belt, is sort of a silly exercise. Your ability to carry a load will depend primarily on the strength and conditioning of your trapezius and deltoid muscles. Most casual hikers have not conditioned these muscle groups in a way that is optimized for carrying a heavy load in a frameless pack. In other words, you condition the muscles by carrying the load. My experience tells me that most folks will find 15 pounds acceptable for long distances (e.g., more than six hours of hiking per day), and 20 pounds acceptable for short distances (a few hours of hiking per day). Those with well-conditioned shoulder muscles can usually accomodate 25 to 30 pounds for short distances and 20 to 25 pounds for long distances. Thru-hikers who have been on the trail for several weeks with a frameless pack may find 35 pounds, or more, acceptable at both short and long distances.
I could never recommend a previous SUL pack such as the Gossamer Gear Uberlite (G6) or the Mountain Laurel Designs Prophet 40 (Spinnaker Version) with weights greater than 25 pounds over long distances and durations. However, I think the Zpacks Blast 18 (even at a similar weight as the other two) would be up to the task, and I’d have no hesitation recommending it for the thru-hiker interested in tackling a Triple Crown Trail, assuming they were intentionally careful with their gear.
Eighteen hundred cubic inches is not a lot of capacity.
It’s generally accepted by our community that it’s just enough for a day or two of food and a simple, ultralight kit of summer gear. My summer ultralight kit easily fits into the Blast 18 without overcompressing insulating gear, and in addition to three days of food, includes a 30-degree synthetic quilt, a torso-sized inflatable sleeping pad, a breathable bivy sack, synthetic insulated jacket, rain jacket, rain pants, a two-person tarp, solo cook kit, and other basic essentials. I keep a windshirt in the back pocket, a water bottle in a side pocket, and lunch in the other side pocket.
In the photos for this article, the Blast 18 is packed with a spring kit for snow cave camping, and includes a 20-degree down sleeping quilt, synthetic insulated jacket and pants, an eVENT bivy sack, a TorsoLite pad, a 3/4-length 5mm foam pad (folded and placed against the back panel), a liquid fuel stove and 1.3L pot, and 1.5 days of food, in addition to basic essentials. My snow shovel and wind jacket (which I’m wearing) go in the back pocket, while food, fuel bottle, and a water bottle get stashed in the sides. The insulation of my sleeping bag, jacket, and puffy pants gets a little more compressed with my spring snow kit, but not enough that I have concern about damaging the insulation.
The outside pockets of the Blast are generously gusseted, so they expand sufficiently for the stowage and retrieval of gear without feeling like you are stuffing your hand into a jar of pudding to find something. The back pocket was plenty big enough to stuff the body of a solo single wall TarpTent into, and the side pockets expanded to easily accomodate a full two-liter Platypus bottle.
Gusseted pockets provide plenty of width for the stowage of bulky gear, but not much height. I was not comfortable putting in a tall, 2-liter Platypus bottle in the pocket, and it ended up coming out of the pocket while bushwhacking. I didn’t really see this as a disadvantage of the pack, so I simply changed my style accordingly and switched to a shorter water bottle. On this trip, I used one packet to pack my lunch and fuel canister (a large Powermax canister), and the other pocket for my water bottle (a 600ml Evernew bottle).
While marketing on the ZPacks website suggests otherwise, items are easier to retrieve out of the side pockets while on the trail than to put back, because of the elastic pocket closures. However, this is no fault of ZPacks in my opinion, but a flawed expectation of the user. With a pack like this, swinging the pack off your back (even while walking, if you have to) and grabbing something out of the side pocket is such a trivial exercise that to belabor the need to access side pocket gear while on the go seems to reflect fundamental incompatibilities with the ultralight ethic. This isn’t adventure racing, this isn’t an adventure racing pack, and it’s not going to be loaded with enough gear that stopping for a moment to remove the pack shouldn’t provide great amounts of disruption to your wilderness experience. If it does, then there may be other problems that have nothing to do with the pack!
When hiking with a pack that weighs only 10 or 12 pounds, swinging the pack off and grabbing the water bottle out of it, rather than inventing new yoga positions to retrieve the bottle from a side pocket, is a preferable modus operandi for me. There is something aesthetically satisfying about tossing a pack on and off your shoulder when everyone else is struggling to load their behemoths to their body.
The Blast 18 will provide enough capacity for overnights and weekend trips for the hiker willing to keep their kit simple and compact, but some discipline will be required in the selection of bulky gear, because volume is limited.
A Note About Packbag Shape and Dimensions
The Blast 18 is symmetrical and uniform, making it an ideal pack for rolling a sleeping pad inside for virtual frame structure. My preference is to fold the pad and wear it against the back panel for padding and to provide some shape that gives the pack more contact surface area with your back, which feels better for carrying heavier loads.
The Blast 18 is a nearly perfect cylinder, which makes it an ideal pack for those that like to pack a foam sleeping pad as a cylinder inside the pack, then stash gear into the middle of the cylinder. I’m personally not a fan of this configuration, but have to admit that unlike most other "shaped packbag" packs that are not cylindrically symmetrical, this configuration works well with the Blast 18. As noted below, depending on perspective, you might find this packbag shape appealing or a liability.
In addition, the Blast 18 carries both small and overstuffed loads well (i.e., a load where the top collar is fully extended, as in the photos), because it maintains a thin, tall shape that does not ride low on the back (an important characteristic of a pack without a waist belt).
- Durable but ultralight fabric.
- Simple, symmetrical design.
- Gusseted outside pockets provide easy access and meaningful capacity.
- Compression integrated into back pocket closure provides gear security on the sides of the pack as well.
- Drawcord closure provides better volume utilization for the weight over roll-top models.
It doesn’t get any simpler than this: a drawcord closure provides the best utilization of packbag volume for the weight, allows for fast and easy access to the packbag, and requires little trim and hardware. Unlike a rolltop closure, however, the drawcord style suffers from lesser protection from precipitation, something that could easily be alleviated if the pack had an option to add a sewn-in top flap or pocket. I dealt with the limitation simply by stowing my gear (as you probably will anyways, regardless of closure type) in waterproof bags. Even in heavy precipitation (rain and wet snow), I never really missed having the roll-top, which surprised me.
- Add-on options provide custom build-to-order pack to suit needs but can result in a very expensive pack and can more than double the weight of the base model.
- No option for a top pocket or flap to extend storage and/or keep water/snow out of the drawcord closure.
- Drawcord closure string is extremely thin and may cut fabric of extension collar over the long term.
- Construction techniques and styling reflect classic young cottage "garage manufacturing". The quality is high and the pack is well sewn, but makes use of simple construction techniques that limit shaping and styling options.
I think it’s important to consider the ZPacks Blast 18 in context with its primary competitor, the Gossamer Gear Murmur (Mountain Laurel Designs was not manufacturing a sub-30L SUL pack at the time of this writing, but they were offering a more richly-featured pack also made with Cubic Tech CTK5.18, the 2009 Revelation, which is heavier and more durable than the previous 2006 model that we previously reviewed).
|Manufacturer/Model||Packbag Volume||Weight||Relative Durability||Suspension||Other Features||Price|
|ZPacks Blast 18||1800 cu. in.||3.3 oz||Excellent (1.5 osy Cubic Fiber CT5K.18)||padded shoulder straps||two side pockets, one back pocket, drawcord closure||$105|
|Gossamer Gear Murmur||1700 cu. in.||7.5 oz||Fair (1.1 osy nylon spinnaker)||padded shoulder straps, webbing waist belt||two side pockets, one back pocket, rolltop closure, pad sleeve,||$80|
|Mountain Laurel Designs 2009 Revelation||2000 cu. in.||6.2 oz||Excellent (1.5 osy Cubic Fiber CT5K.18)||padded shoulder straps, winged hip belt, sternum strap||two side pockets, one back mesh pocket, rolltop closure, cord compression||$170|
The relative strengths of the Blast 18 are its weight and durability, while the Murmur offers more features at a lower cost. The Revelation offers greater capacity, more refined styling, and when compared to the scenario of adding options to the Blast 18 that match the features of the Revelation, the Revelation comes in slightly less expensive.
Unfortunately, I find it hard to justify spending more than $100 on such a small pack that requires little in the way of sophistication to effectively carry light loads, but in the absence of other options, my personal choices do lean towards the more durable packs, because I’m more confident of their longevity, an important consideration for me as I continue to pursue a lighter and simpler lifestyle.
I found myself not wanting much after using this pack. I did replace the drawcord closure with a thicker string because I have found very thin strings abrade and cut through Cubic Tech fabrics over time. The weight penalty for replacing the string was negligible.
My only complaint with the pack is in its packbag shape. While the sausage design (symmetrical cylinder) works well for enclosing a rolled-perimeter sleeping mat (into the center of which gear is stowed for stability), it’s not particularly stylish and doesn’t rest against your back when fully loaded as well as it could. Carrying the Blast 18 stuffed to its gills feels a bit like hauling a log on your bag (albeit a soft, light one), because it does sort of roll and bobble here and there. I was able to mitigate this effect somewhat by folding my foam pad into thirds and using it as a virtual frame against the back of the pack, but for this to work most effectively, I would have prefered a slightly wider packbag. In addition, I’m a fan of packbags that taper from a smaller cross section near the bottom to a larger cross section near the top, because they accomodate widely varying load capacities a little better (although, this is less of an issue with such a small volume weekend pack like the Blast 18).
Photos: Ryan and Stephanie Jordan; Olympus E-510 Leica Summilux 25mm/f1.4.