Vibram FiveFingers KSO Review
Cons: Very particular sizing, lengthy break-in time, goofy looking
Our Analysis and Test Results
The KSO is the closest thing to the original FiveFingers design, with minimal outsole padding and a zero-drop ratio. "KSO" stands for "Keep Stuff Out," and the hook-and-loop closure fastens tightly around your foot to prevent rocks and sand from getting inside — a huge improvement over the original FiveFingers shoe. This shoe nearly perfectly emulates the natural shape of your foot. Combined with its tacky, non-marking sole, it's almost as if you developed naturally sticky, Spider-Man-like feet.
As the original and still one of the best designs on the market, the KSO is essentially a foot-glove and rightfully provides an accurate barefoot experience. A lightweight upper wraps seamlessly into a 3.5mm outsole in a way that feels like you're pulling on a heavy-duty sock. Considering that the ultra-thin microfiber insole is sewn-in directly and that there is no midsole, you can expect to feel every bump in the road. The outsole is slightly thicker under the ball of the foot, working three-fold: to beef up the natural rocker in the ball of your foot, to act as a bit of a brake running downhill, and to provide just enough extra protection from thorns and sharp rocks.
While we always suggest visiting your local shop in person to find the right fit, it's even more important to size the KSO properly. In order to minimize the chance of hot spots and blisters, we also highly suggest purchasing a pair of toesocks — our testers are big fans of Injinji socks, even if we're not wearing FiveFingers shoes.
The 360-degree, single hook-and-loop velcro closure of the KSO pulls your foot firmly into position, bringing the heel-cup right up against your Achilles and your toes right to the front of their individual boxes. The FiveFingers design allows for individual articulation of the toes, which translates to improved grip and a natural boost when running. Although the FiveFingers shape might suggest that these will fit any foot, they seem to best suit those with narrow to mid-width feet — those with particularly wide feet might find the closure system to be uncomfortably tight.
From the company that helped define minimalist footwear, the FiveFingers KSO provides little more than a protective foot wrap. Weighing in at only 5.5 ounces per shoe, these are rightfully one of the lightest shoes we tested.
Combine this with outstanding barefoot accuracy, and it should come as no surprise that wearing the KSO doesn't feel like much when you have it on. We wouldn't exactly describe the fit as airy, though this simple design is lighter even than most sandals. However, even when soaking wet, they are incredibly lightweight. Heel loops allow you to clip this ultralight pair of shoes onto a waist belt and present an interesting option for close-toed river shoes for warm water anglers.
Despite its foot-mimicking pattern, the XS Trek outsole is not nearly as grippy as it is flexible. The proprietary, non-marking rubber is tacky enough for any gym floor, and the enhanced flexibility helps you naturally grip with your toes on trails or rough terrain. But even if it's just a little damp out, be ready for some proprioception training. With an essentially smooth bottom, the KSO slips and slides over wet surfaces, whether those are rocks or concrete. If you live and exercise in any climate where it regularly rains, we suggest looking at other shoes in this review.
The FiveFingers KSO is designed as a versatile outdoor shoe, but we actually find it's more suited to a life in the gym. The tacky Vibram XS Trek outsole climbs well enough on dry, rocky trails, but when it comes to running or walking over wet surfaces, even wet concrete, the lack of lugs or wells to shed water left us slipping and sliding all over the place. The stretchy, polyester upper is designed much like a water shoe and dries equally quickly. With their low-profile design, these would make great companions for river crossings on backpacking trips — just make sure you give the soles a quick wipe before trying to scramble up the rocks on the opposite bank. Style comments aside, these are indeed a serious barefoot shoe and should not be considered as an easy way to transition into this running style.
Despite a fairly simple structure, the quality and durability known to Vibram soles extend through the rest of KSO. Areas that often see the most wear-and-tear — around the ends of the toe box(es), the heel, and around the sides — are provided additional support thanks to a wrap-around sole. Additionally, the sole is glued and sealed to both the heavy-duty Hypalon that acts as a quarter stiffener and the abrasion-resistant polyamide upper. After running miles of the rough sand arroyos that stripe the Southwest, these shoes emerged practically spotless.
The KSO is certainly a specialty shoe. But for those who firmly believe that barefoot shoes are the basis for holistic training, this classic will continue to impress and sells for a very reasonable price. While not as versatile as other trainers we tested when it comes to bridging the gap between road and trail, these true barefoot shoes will surely help you train proprioception and gait.
If you are looking for an authentic barefoot experience and have the confidence to stand up to a few sideways glances at the gym, then you likely already know the secret of training in a shoe like the Vibram FiveFingers KSO. While other companies have certainly improved on barefoot shoe design, these classics still stand up to the test of time.
— Aaron Rice
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