for the love of bare feet and vibram five fingers shoes.

Back in September, I first got my feet in a pair of the kangaroo leather-clad, aggressively-lugged Five Fingers KSO Trek (See me unbox the Vibram Five Fingers KSO Trek here and also my first impressions after a trail run in Trek FiveFingers [initial review] here). Since then, I've mostly been testing them as my everyday VFFs, but I've also had the chance to hike and run in them.

Though I'll go into more detail on the KSO Treks below, in short, the Treks are a compelling, ground-breaking product that take the minimalist Five Fingers foot glove model, add super-comfy, water-resistant leather (though in total the Treks aren't waterproof), and adapt it for the type of terrain you get out in nature. Compared to standard VFFs, the Treks provide a smidge of added comfort on the trails through an ever-so-slightly thicker sole and a bit of EVA. Meanwhile, they are the most aesthetically acceptable, least freaky of the Vibram Five Fingers family. In black or brown suede-up kangaroo leather, the Treks marry form and function — they're the most likely VFFs to go unnoticed in public while allowing you to outrun a bear in the woods — in theory and if you're really fast, anyway*. If you want to pick up a pair, you can grab some over at CitySports.

KSO Trek — Design and Aesthetic:

Two factors stand out as distinguishing characteristics of the KSO Trek as compared to the standard KSO: the lugged sole, which includes 4mm EVA to protect against "stone-bruising," and the use of kangaroo leather as the main material.

The sole of the KSO Trek (Image: KSO Trek sole) has an aggressive tread that utilizes plus-shaped Vibram rubber "cleats," is beefiest and most rugged at the midfoot, and culminates at the toes with angled, ridged toes. In my testing, this tread definitely provided improved grip on loose or muddy terrain as compared to the standard VFF sole. Razor siping simply doesn't do much for your feet on ground that gives underneath your weight. I found the KSO Treks inspired confidence while bounding up steep grades at a local natural wooded park here in Atlanta.

That said, as ultra-runner Leif Rustvold put it, "[T]he Treks sacrifice a certain amount of the dynamic grip I’ve come to enjoy for the static grip of their increased tread." On the flipside, Leif remarked that in the KSO Treks he was able to "bomb down a trail" similar to how he would in traditional shoes.

As with all treaded shoes, mud can gunk up the works. That said, my KSO Treks cleared mud fairly quickly as soon as they had the chance to tread on hard packed or just less muddy ground or rockbeds.

Despite the added thickness of the KSO Trek sole, there is still a remarkable amount of information transferred from the ground to the foot. It's less than you get with KSOs, which is less than you get with Classics, but it still beats the pants off a regular shoe.

I took a few measurements at the heel, arch, and forefoot of the KSO trek and the KSO using skinfold calipers. Though I found it difficult to get consistent measurements, the chart below should give you some idea of not only the difference in thickness between KSO Trek and KSO, but also in the compressibility of the 4mm EVA midsole in the KSO Trek.

Note: I measured the heel thickness at one of the plus-sized lugs on the Treks. The forefoot thickness was measured at the row of tread behind the toes of the Treks. Similar points were measured on the standard KSOs

The lugged sole compresses comfortably on smooth surfaces (You won't feel the cleats poking you) making the KSO Treks comfortable for use on the trail, running on asphalt, or just bounding about around town or at work. By the way, if you're wondering, the EVA is easily discernible on the brown KSO Treks — it is that greyish material between the black Vibram sole and the leather (Seen in profile here).

One word of caution: the ridged toes are designed not only to snag the earth, but also to allow for upward flex of the toes. Perhaps unavoidably, this combination of grip-ability and flexibility is accomplished by way of a thin line of Vibram rubber at the base of each ridged toe that separates the toe ridges from the rest of the sole. This may be a weak point on the soles as one forum member has seen the rubber tear here (See this image from Kevin | forum discussion here).

As far as the kangaroo leather is concerned most will find it a welcome addition to the KSO Trek line. Not only is the leather buttery smooth, feeling great on your feet (The footbed is also leather), it is water-resistant (Not waterproof but the kangaroo leather does not hold water), breathes better than the synthetic material found in other VFFs. It's also intended to be durable enough to prevent snags and tears. I've not experienced any snags or tears nor have I seen any from users to date, so the stronger leather material does seem to make the Treks more durable for hard conditions.

It's also been my experience with natural materials like leather that they are less likely to acquire odors. To date, my KSO Treks have not acquired the feared VFF stank.

There have been some sole-to-leather adherence issues where the soles are detaching at the edges from the leather upper. To the extent that this has happened, wearers have re-glued using Shoe Goo or some other adhesive. If I had to guess, this is probably due to the innate problems of binding unlike materials — particularly leather. I've seen it a bit on the heels of my Treks, but it hasn't caused any problems. Hopefully, this issue will be addressed

From an aesthetic point of view, the KSO Treks are the most incognito FiveFingers to date. They look the most shoe-like and leather says "expensive" more than it says "weird." Wearing the Treks around town, my VFFs tend to go unnoticed—not sure if I like that or not, but this could be welcome to many who tire of having their feet constantly stared at by strangers!

For casual style, I like the look of the KSO Treks with cargo pants (and stroller) as seen here or perched on a rock in the VFF Treks amidst a hike here. If you're workspace is a bit more casually inclined, there are some who are sporting their Treks on the job (See Alan at work in Treks and Luis at work in Treks).

KSO Trek — Performance

Managing a creek bed on a hike in the Smokey Mountains in the KSO Trek FiveFingers.

The whole point of the KSO Trek, in addition to some stone-bruising protection, is "improved traction on trails and over more rugged terrain." I've used my Treks for hiking, trail running, and everyday wear.

On the trail, the Treks deliver as far as providing added traction on mud, steep inclines, and varied terrain. I found myself bounding up steep embankments with considerably more confidence than in the laser-siped standard KSO FiveFingers. I also noticed a bit less poking and prodding from random ground protrusions thanks to the compression and cushioning, as minor as it may be, from the EVA.

Again, the KSO Trek is not waterproof and water will seep into the toe pockets at the seams and through the synthetic material on the sidewalls of each toe. Even still, the additional ground clearance you get with the Treks combined with the overall use of the amazingly water-resistant leather combines for a less soaked VFF when crossing the odd creekbed.

A few VFFers have already put their Treks to somewhat extreme tests on the trail and/or road and their experiences have been overwhelmingly positive:

• Barefoot Ted ran the Leadville 100 ultramarathon in KSO Treks
• Leif Rustvold ran a 100 mile ultramarathon in his FiveFinger Treks
• Juergs ran a 50K in his KSO Treks — Also, see Juergs' training notes
• Chad ran a marathon in KSO Treks — see Chad's initial thoughts

All in all, I've yet to find someone who wasn't satisfied with the performance of their KSO Treks.

KSO Trek — Overall thoughts

I think the FiveFingers KSO Trek will have a permanent place in the Vibram line-up due to its impressive combination of design, performance, materials, and aesthetic — all while maintaining a minimalist form-factor (The KSO Treks weigh in at under 6 oz/each "shoe" and under 12 oz total). I find myself wearing my Treks frequently nowadays for just bumming around.

At $125 MSRP in the U.S., the KSO Trek is not cheap, unfortunately, but if you're savvy, you should be able to find a pair on sale from a local retailer or on the internet (So keep your eyes open and shop around!).

KSO Trek — Sizing and other considerations, including KSO Treks for Women and Small-footed men

The KSO Trek sizes the same as the standard KSO with one caveat. I'm a size 43 in KSOs and I find my size 43 KSO Treks to fit exactly the same—except they are a bit more snug on the top. Unlike the KSO's stretchy synthetic fabric and mesh-upper, the KSO Trek upper is less-stretchy leather. In order for the KSO Treks to accommodate different insteps, the Trek stretches by way of slits in the leather which are bound together with stretchy synthetic material (Described as the "sock liner," see this photo and note the lines going away from the ankle — those are the slits).

On socks: many have asked if you need to size up for socks. Like most VFFs, sizing up to accommodate socks is unnecessary — exceptions being if your VFFs are already very snug (toes right up close to the end of the pocket), socks may be the "last straw" that make your feet too big. If this is you, it's highly recommended you try on a pair in person first to figure out sizing!

Overall, the KSO Treks are more snug on top of the foot compared to the standard KSO. This may be a concern for you if you have KSOs or Sprints and already know you have a high instep, typically denoted by how far the strap crosses back over the top of your foot. Forum member desaulniers covered this in a helpful video comparison of the KSO Trek with the KSO.

As of the date of this review, the Five Fingers KSO Trek is only available in men's sizes from 40 - 47. Thankfully, Vibram will be releasing the KSO Trek in late spring 2010 in women's sizes and additionally in size 38 and 39 for men (see the KSO Trek for women announcement discussion here).

For now and the foreseeable future, the KSO Trek is my go-to trail shoe and my go-to dressy pair of Five Fingers. If you are on the fence, grab a pair already!

Additional reading:

• Unboxing the KSO Trek (Video), initial thoughts, and photos
• First trail run in the Five Fingers KSO Treks
• BirthdayShoes Forum discussion of the KSO Trek
• Women's KSO Treks greenlighted for production by Vibram
• The official KSO Trek page at VibramFiveFingers.com
• Pick up a pair of KSO Treks at CitySports.com!

If you have any questions about the Five Fingers KSO Trek, or would like me to go into further depth on a particular part of this review, please leave feedback below.

My KSO Trek-clad feet amidst some fall leaves after a hike in the Smoky Mountains.

* Do not take my advice as far as what to do when approached by a bear.

Disclaimer: CitySports is an online retailer that supports BirthdayShoes by way of affiliate links. Any purchases you make through CitySports links will go to supporting this VFF fan community!