One of my goals for this winter has been to switch to a more comfortable, lightweight mountaineering boot without a removable liner, at least for day hikes. While my other pair of plastic boots, Scarpa Omegas (5 pounds 2 ounces/pair), are probably the lightest weight and most comfortable boots with a liner (no longer made), they still feel like you’re wearing cinder blocks on long approach hikes – a not-to-uncommon sensation with plastic boots.
While boots with removable liners are often required for overnight trips where you can’t risk having your boots freeze from the previous day’s foot perspiration (up to 8 ounces per day per foot), they sacrifice fine motor control and climbing feel on more technical routes because they’re so much larger and wider than mountaineering boots without liners. Since most of my winter hikes are day trips and also require very long approach hikes or snowshoeing, I am ready to lighten up and try a smaller volume boot.
At 4 pounds 6.5 ounces/ pair, the new AKU SL Pro II GTX Mountaineering Boots looked like a good candidate to try. AKU is an Italian boot maker best known for their Spider Kevlar GTX boot, a bomber ice climbing boot that is known for its comfort on long approach hikes. Comfort on approach hikes is a usually a function of rocker, or a slight lengthwise curvature of the sole ,which makes walking more natural.
Though not as warm as the Spider which is rated for 6000 meter alpine summits, the SL Pro II GTX is rated for 4000 meter ascents and ice climbing. It is insulated using Gore-tex Duratherm, a hollow fiber insulation laminated to a waterproof liner which ensures warmth and breathability, and is used by many other mountaineering boot manufacturers. In addition, the SL Pro II GTX comes with an aluminum coated footbed designed to reflect your foot’s body heat back into the boot and which prevents it from being radiated into the ground.
Although it’s still early in the winter season, I have already used the SL Pro II GTX boots for long approach hikes in snow and steep climbs over mixed rock and ice, which is typical for the White Mountains of New Hampshire where I spend many of my weekends in winter.
Structurally, the AKU SL Pro GTX II’s are very rigid, which is desirable for a boot rated for step-in crampons. The rigidity comes from an exoskeleton adhered to the outside of the boot, high rubber front and heel rands for protection, and a carbon fiber last which is lightweight but extremely stiff. This translates into excellent control, particularly for climbing on steep, dry rock, something I don’t get with my much higher volume plastic mountaineering boots.
Fit-wise, the boot is much lower volume than a boot with a separate liner, but it also has fantastic arch support eliminating the need for the superfeet insoles which many of us turn to provide extra support or to use up extra volume in mountaineering boots. The fit around the toes is noticeably narrow, while wider around the heel, which may require some creative sock shimming depending on your foot shape.
For myself, I found the best combination is to layer a liner sock over a medium weight wool sock that I’ve cut the toes off of to keep my toes mobile, but take up the extra width around my heel and ankle. This lets me also add a vapor barrier liner as a base layer so I can use the AKU SL Pro II GTX for overnight trips, but that requires a separate article at a future date.
I am pleased with the performance of the AKU SL Pro II GTX boots so far and look forward to many big hikes with them this winter and beyond.
Disclosure: Philip Werner (SectionHiker.com) received a complementary pair of AKU SL Pro II GTX Mountaineering Boots for this review.
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