Zpacks Arc Blast

This is a great UL pack that is smartly designed, comfortable within its load limits, customizable, and about as light as you will find in a framed midsized backpack. Cuben and carbon fiber construction keep the weight at around one pound.

This is a review of the Zpacks Arc Blast backpack. I purchased one in late Spring 2014 and have had the opportunity to put a couple hundred miles on it by now. I am not associated with Zpacks in any way.

This is probably the lightest framed mid-size backpack on the planet, thanks to the use of cuben fabric, carbon frame rods, and minimalist design. The 52L model, which is what I have, specs at only 16.5 ounces. It easily holds a full-sized bear canister along with all my gear. Load capacity is stated at up to 30 pounds, and I found this to be accurate when carrying up to about 28 lbs and started to feel the comfort decline. The pack could haul more than that but comfort will suffer.

The pack fabric is a cuben hybrid, which is a layer of cuben on the inside for tear strength bonded to a thin 50d polyester outer layer that protects from abrasion and provides color and opacity. Currently the pack is offered in six colors – orange, blue, gray, green, black, and camo.

Because of its use of cuben fabric and UL construction, this pack is not going to be the most durable, but Zpacks states that it should last for at least one long thru-hike (AT/PCT/etc).

Rather than coming in S/M/L torso sizes, the Arc Blast is custom-made to fit you. Their website has instructions how you should measure yourself, and the torso will be sized to you, in one-inch increments. Manufacturing can take 2-6 weeks, depending how busy they are, so if you want one for a specific trip be sure to plan ahead.

The Arc Blast has fully taped seams and a roll-top closure, so the pack is waterproof. This further saves weight by eliminating the need for a liner or pack cover, though certainly continue to use one if that makes you more comfortable. FWIW I've been caught in a couple of steady rains without any liner or cover and the inside of the pack stayed completely dry.

The pack's frame is made from four feather-light carbon fiber rods, two placed vertically for support and weight transfer and two horizontally for stability and better structure. The rods are held in place by "sleeves" that they fit into, so they can be taken out if you prefer. Overall the pack does a decent job of transferring weight to the hip belt.

A distinguishing feature of this pack is the "arc" that gives it its name – the carbon rods can be flexed to form an arc that leaves an air gap across your back. I happen to love this feature, though I recognize that some people do not want their pack pulled away from their body.

You can adjust how much flex you want, including having none at all, but keep in mind that the pack was designed to be optimally comfortable with a flexed arc setup. To me it carries extremely well — airflow through the arc gap means no more "sweaty back", and the load still holds an overall tight center of gravity.

Padding on the Arc Blast is decent, somewhat thin and dense foam is inside the shoulder straps and inside the hip belt. The shoulder straps and hip belt are stitched with daisy-chain loops for attaching accessories. The sternum strap buckle does not include a signal whistle.

The standard configuration includes two side pockets made of cuben fiber with angled openings and elastic at the top, and one large mesh front pocket. Zpacks is glad to change this configuration and materials if you want. I have found the side pockets to be fairly easy for taking out and, more to the point, putting back a water bottle while wearing the pack. The pack does not come with hip belt pockets, though these can be purchased separately. Nor does it come with any inside storage pocket, though again Zpacks will add one to your specs if you like.

EDIT: I want to add that, while I found the pack to be waterproof, the Zpacks hip belt pockets are only water resistant. I think it is because the zippers (which are listed as "waterproof" zippers BTW) face straight up/skyward, allowing the rain fall directly on them. In steady rain the insides of my belt pockets got a little wet, definitely not soaked. I had my camera in there and it was fine, but after the first time this happened I now also carry a little ziploc bag in there as well, so when it rains I put the camera inside the zip bag and then I am confident that is safe inside the belt pocket.

The pack also includes a top strap and a pair of bottom straps for lashing on something like a sleeping pad. The sides of the pack are zigzagged with thin (approx 2mm) cord to provide compression and help hold tall or loose items on the sides. You can add similar cord to the back for more load control, though I have not found it necessary.

As configured the 52L option is $279, also available is a "slim" 45L model ($275) and a wider 60L ($289). All three pack bodies are the same height, it is variations in the front-to-back depth that provides the different capacities. There also is a zippered model in 3 different sizes that opens like a panel loader, if that is your preference.

I modded mine a bit, opting to not have a hydration tube port and adding hip belt pockets, lumbar pad, and load lifters. I chose a pair of the Zpacks hip belt pockets (0.75 oz each, $22 for one or $42 for a pair). These pockets are huge, about one full liter per pocket. I load them up with all the little ditty stuff that would have gone into little pockets or sacks on the inside of my pack, now they are at my fingertips – camera, PLB, first-aid, snacks, pencil and paper, headlamp, head net, etc.

They do bulge out when stuffed full like that, but I have found that having everything at my fingertips, without having to take off the pack, is well worth it. I do keep the pockets clipped as far to the front of the hip belt as possible so that they aren't in the way of my swinging arms.

All in all this is a great UL pack that is smartly designed, comfortable within its load limits, customizable, and about as light as you will find in a framed midsized backpack.