Vibrams’s Five Fingers KSO is the current gold-standard by which all other minimalist shoes are measured. I have used this shoe extensively for about three years in many different conditions. It is my default gym shoe, my winter running shoe, my asphalt-too-hot-for-barefoot shoe, and the shoe I wore to finish my first 100 mile race in September of 2009. This model has served me well and is still my preferred minimalist shoe, but does suffer from some minor faults that prevent it from being the Holy Grail of minimalist running shoes.
When I first received my KSOs, my first impression was one of wonder. They are so different from any other shoe on the market, one cannot help but to appreciate the design. The individual toe pockets give them a style that is both distinctive and functional. The weight is light compared to traditional trainers, and close to the weight of most racing flats. The sole is very thin… I believe it is approximately 3mm thick down the entire width of the shoe. The sole is made of a rubber compound that wears well. I have about 600 miles on my original pair and I can still see the tiny grooves cut into the soles. The upper is a combination of stretchy fabric and mesh. A single velcro strap wraps around the heel and over the foot to help secure the shoe to the foot. Construction quality is very good.
When I put them on for the first time, I was surprised at the comfort. The shoe is designed to fit the exact shape of your foot. I would compare the it and feel to wearing a glove on your foot. Some people have reported being annoyed with the feeling of fabric between the toes, but I did not mind. I adapted to this feeling within a few minutes.
Putting the Vibrams on for the first time was somewhat difficult. Getting each toe in the right toe pocket takes some practice. After using the shoes extensively for a few years, I have mastered this particular skill. Wet feet can make the process more difficult. I will sometimes wear my KSOs with Injinji toe socks, which seem to make them somewhat easier to put on.
The feel of Vibrams on your feet is difficult to describe until you experience it because there really is no other shoe that closely approximates the design. The KSOs allow your foot to move as if you were barefoot because of a close fit coupled with flexible design. It really feels as if you are wearing a glove on your foot. I normally wear a 10.5 or 11 shoe size (US sizing). My first pair of KSOs are size 42 which fit my feet perfectly. If socks are worn, they are slightly constrictive. I also have a size 44 which are quite large. I purchased this pair to accommodate foot swelling when running long ultramarathons. On the larger size, my smallest toe sometimes falls out of its toe pocket. This doesn’t seem to influence performance in any way.
The width of the shoe is sufficient for my feet, but my feet are rather narrow. Some individuals with wide feet may have some difficulty with this particular model. The width and individual toe pockets allow the toes to splay when running which is a critical component of barefoot running.
Walking in KSOs is a pleasant experience. When I walk barefoot, I never use a heel strike. In KSOs, I have a slight increase in heel strike walking. This is probably due to the lack of tactile sensation with the ground.
Running is where these shoes really shine. I always prefer to run barefoot. This shoe is the best alternative I have found. It’s not a close approximation, but the flat, thin sole and flexible design allow the foot to work in a way that is somewhat similar to running barefoot. The thin sole is a major advantage over other shoes on the market, but Vibram apparently added another layer to the sole after the first generation of KSOs. This added layer decreased both ground feel and flexibility. This may have made the shoe more appealing to runners moving from traditional trainers, but was a regression for barefoot runners.
Traction on dry, hard surfaces is excellent. The rubber soles are both durable and “sticky.” Traction on wet surfaces is still decent. It is similar to other traditional trainers. Traction on dry trails is also very good. Muddy, snowy, or icy trails are a major obstacle for KSOs. Traction is horrible in these conditions. Personally, I don’t mind training in these conditions as it is a good strengthening activity. However, racing would be VERY difficult.
Ventilation on this shoe is excellent. The fabric and mesh upper dries quickly and allows moisture to drain. I would compare the KSOs ventilation to most trail running shoes. The ventilation also helps keep the shoe relatively cool in warm weather. While my feet will sweat, it is not excessive. In cold weather, I find the shoe itself to be sufficiently warm. I’ve worn the shoes without socks for 20 mile runs in temperatures around 10 degrees (F). I have combined the shoe with socks to keep warm in temperatures several degrees below zero. As long as I am running, my feet do not get cold. My feet will get VERY cold when stopping for more than a few minutes.
This shoe can be worn comfortably for very long periods of time. I have used them for several training runs of six to eight hours, and wore a pair for my 29 hour 100-mile finish.
One are of concern is smell. After about six months of use, my KSOs developed a bad odor. It was different than the typical and familiar “shoe stink” other shoes experience. This smelled a bit more like a rotting corpse. At first I assumed it was a function of my own feet. Then I smelled other peoples’ KSOs (all in the name of a thorough review.) They smelled the same. I have attempted many methods to rid my KSOs of this overwhelming odor. I’ve washed them in a variety of detergents, sprayed with Febreeze, soaked in a bleach and water solution, soaked in a vinegar and water solution, left them in the sun, stuck them in the freezer, used medicated foot powders, and used effervescent denture cleaner tablets. To date, only the denture tablets and freezing seem to keep the odor at bay. Even this is just a temporary solution; the smell returns after one or two runs. The odor problem is not an issue for running. The problem arises at the gym. The smell is very noticeable up to about a six foot radius. This causes me to hesitate when wearing them in close quarters. It’s not a deal-breaker, but I do consider it to be a major problem.
In conclusion, I would rate Vibram’s Five Fingers KSOs as very good to excellent. There is room for some improvement, but these shoes stand as the current best shoe option for barefoot runners needing some protection. This shoe will work well for most people, but it may be useful to try them on before ordering. The individual toe pockets may not work for all feet. Vibram could solve a few small issues with this shoe. Otherwise, I would give this product my stamp of approval.