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.
The Acrux was a favorite boot on colder days.
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 2oz (or 965g) for one boot on our freshly calibrated scale.
It is one of the heavier boots in our review; in the same general weight range as the Scarpa Mont Blanc Pro and the La Sportiva Nepal Cube. Both of which are less warm and weather resistant.
The three boots with super gaiters in our test. The Acrux is the heaviest but the only one with a removable inner boot.
The Acrux 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.
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 Acrux is much warmer than the next two warmest boots in the review, the Scarpa Phantom Tech and the La Sportiva G5.
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 have used this boot for six 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 isn't forced to warm up the cold boot.
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 can't be beaten, the only way your foot is getting wet is if water comes in over the top of this 12 inch (30cm) high boot. In our tub test, it tied with the Phantom Tech for water resistance.
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.
Waterproofness testing. We stood in this creek for over a minute. No water got inside.
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 (this is also a benefit when employing French technique on moderate slopes). We also felt that the slightly flexible sole helped on dry rock without crampons.
On the ice this boots performance was average. 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 calf support for steeper pitches. We felt the same on mixed terrain or when dry-tooling: performance was not bad but nothing special.
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. Climbers whose only priority is steep ice in cold weather should consider one of the super-gaiter boots, like the Scarpa Phantom Tech.
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.
Our testers were pleasantly surprised by how comfortable this boot is for hiking. While it's certainly no cushy trail runner, it performed better than some much lighter boots. We think the slight flex in the sole helps counteract the weight of this boot when we're hiking on trails.
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.
The lacing system of the boot is good. Traditional laces cover the forefoot and up to the ankle with no lace lock. The upper part of the boot is secured with a power strap. As mentioned, our testers really like the power strap for quick adjustments. The Acrux requires as many steps for closure as the G5 but isn't quite as fast to adjust.
Damage to our second boot after one day of ice cragging, the rand is separating from the rest of the boot toe.
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.
At $750, this boot is priced similarly to super-gaiter boots and is cheaper than other modern double boots.
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 with two pairs of this boot. Arc'teryx responded promptly, and we haven't had a problem since. 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.