What makes the Arc'teryx Acrux AR unique is that it's the lightest double boot on the market. Instead of being a double boot made for 6000m peaks (with the associated insulation and bulk), it's a double boot made for 4-5000m peaks. This means that this boot is much more pleasant to hike and climb in than its 6000m brethren.
Performance Comparison
The Acrux was a favorite boot on colder days.
Weight And Bulk
For the most part, companies list the weight of one boot (or 1/2 of a pair) in a size 42. Many of the online sources of information on this boot, including the Arc'teryx website, list different weights. Our tester pair is size 43 and 1/3 (Arc'teryx labels their Euro sizes oddly, this is the equivalent of a 9.5 US men's) and weighed in at 2lb 1.7oz (or 955g) for one boot on our freshly calibrated scale.
This is only a few ounces less than modern 6000m double boots. While we appreciate the slight weight advantage, our testers really noticed the difference in the overall size of the boot. When measured around the fullest part of the forefoot, the Acrux is about an inch smaller than the La Sportiva G2SM.
Rock Climbing Ability
The Acrux AR climbed rock well for a double boot and was only slightly lower performing than the super-gaiter boots in our test. Ankle flexibility is essential for rock climbing; we liked that the boot gave us the option to quickly increase the ankle flex by loosening up the velcro ankle strap. The sole of this boot is relatively thin; it's about as thick at the toe as the La Sportiva Trango Ice Cube, which helped with both sensitivity and balance, as it kept our toe close to the rock.
We liked the ability to quickly unzip the gaiter and adjust the tension on the ankle strap; loose for hiking and snug for steep climbing.
Ice Climbing Ability
We were expecting the Acrux to perform well on the ice - and it did. We had good crampon fit with Black Diamond, Petzl, and some Grivel toe bails. While the ankles on the Acrux AR aren't as supportive as our favorite boot for front pointing, the La Sportiva Nepal Cube, there was sufficient ankle support for steeper pitches.
Grivel G12 (top), BD Stinger (bottom left), and Petzl Lynx (bottom right). Note the suboptimal fit on this Grivel bail.
Our larger testers detected some flex in the soles of this boot when on their front points, and in fact, Arc'teryx acknowledges that it was designed with a less than fully rigid sole for improved performance on approaches. Sole rigidity is a balance between front-pointing performance and hiking and rock climbing performance. Climbers whose only priority is steep ice in cold weather should consider one of the super-gaiter boots.
Hiking Ability
Our testers were pleasantly surprised with how comfortable this boot is for hiking. While it's certainly no cushy trail runner, it performed as well as either of the super-gaiter boots in our review. The sock-like fit of the inner boot kept all blisters at bay, regardless of approach length. Once again, the convenience of the velcro ankle strap let us hike with the ankle of the boot reasonably loose, but the laces snugged up.
Warmth
This is a category where the Acrux AR shines. Many factors well beyond boot construction contribute to how warm our feet feel. Nonetheless, our testers felt that this was the warmest boot in our review. Insulation comes both from the removable liner boot and the inner shell. Any boot with an integrated super-gaiter construction will be warmer than one without, because the gaiter traps heat, and that's certainly the case here.
The sock-like inner boot of the Acrux. Note the pull loop at the heel, it's essential for getting the inner boot off.
We used this boot for two separate five-day trips over 14,000 feet (4200m) in the winter. Both times our feet were warm for the whole trip, even summit day. That's because each night we were able to pull out the liner and bring it into our sleeping bag to dry. With any lightweight, single, or super-gaiter boot, drying the boot out each night would have meant spending lots of time cleaning all of the snow off of the exterior before bringing it into our bag. Even then there would be two rigid objects in the sleeping bag with us, which is not a comfortable proposition. The other advantage of having the liner in your sleeping bag is that in the morning, your foot is forced to warm up the cold boot.
Waterproofness
A dry foot is a comfortable foot. Because of the gaiter, super-gaiter boots are inherently more waterproof. Maybe it's just because Arc'teryx is based in rainy Vancouver, but for waterproofness, the Acrux beat out both the Scarpa Phantom Tech (because its waterproof zipper sometimes opens unexpectedly) and the La Sportiva G5 (because its zipper isn't waterproof).
Waterproofness testing. We stood in this creek for over a minute. No water got inside.
The liner boot of the Acrux has a Gore-Tex membrane. The gaiter of the shell is also constructed with Gore-Tex and has a waterproof zipper. The top of the gaiter has a built-in drawcord to seal it around your legs and keep out snow. If snow coming in is a concern, we think the best plan for this boot isn't to tuck your pants into it, but rather to let them drape over and keep that drawcord tight.
Durability
This was a category that gave our testing team some doubts. The construction feels very durable throughout. Often the gaiter of a super-gaiter boot wears out quickly where it rubs against something on the inner shell. The gaiter on the Acrux is reinforced where it rubs against the velcro strap, which is a nice touch.
Damage to our second boot after one day of ice cragging, the rand is separating from the rest of the boot toe.
However, the first pair of tester boots we purchased experienced some serious sole delamination after six days of use. With the second pair, we began to get separation between to toe cap and the rand after one day of ice cragging. We can't find any other climbers experiencing similar problems with this boot and have generally had good experiences with other Arc'teryx products, so we're willing to chalk this up to bad luck and hope that pair three will be perfect.
Best Applications
This is a great boot for anyone venturing into cold technical terrain, as it's particularly good in foul weather. It shines on overnight trips, and is an excellent tool for climbers venturing out for multiple days in the winter.
Value
At $750, this boot is priced similarly to super-gaiter boots and is cheaper than other modern double boots. We think that if the two major flaws we experienced are isolated incidents, then this boot is a good value.
Conclusion
The Arc'teryx Acrux is the warmest boot in our review. A removable liner on a boot designed for altitudes less than 6000m is a unique and advantageous feature and gives this boot a level of versatility not found in comparable products. We experienced some serious durability issues but hope that they're not widespread. While this isn't a perfect contender for cold weather ice climbing, it does get the job done, and its other attributes make it uniquely qualified as an all-around cold weather mountain boot.
The Acrux in action.
