La Sportiva is perhaps best known for its Nepal Extreme leather single mountaineering boot. Used by generations of mountaineers worldwide, it has become a true classic. The K4S is the company's latest offering, attempting to gain the same popularity for a mostly plastic single-boot. It's targeted at generally the same market as the Extreme - winter mountaineering, alpine rock and ice, technical mixed routes and waterfall ice climbing.
The boot is speced at a very svelt 4' 15 ounces. We had a postal scale sitting around so we decided to check the actual weight. Our test pair, a size 44 1/5 Euro, came in at 5'. That prompted us to check our other boots for comparison.
||4' 15 oz.
|Koflach Arctis Expe
||5' 8 oz .
||6' 8 oz.
|All boots are the same size and weight is for
a pair of boots.
Any way you cut it, the K4S came in a full pound under our Extremes and a pound and a half less than the Expe's. Not too shabby! I hate hauling anything up a climb I don't have to and lighter makes the hiking easier, so this is a real plus.
The fit on the K4S is definitely different from the Extreme. The back of the boot is narrower and seemed to hold my heel more tightly. The front of the boot is a bit wider, providing more space for my toes. This kept my toes a little warmer and more comfortable. I've had a problem for years with my big toe on my left foot banging into the front of my boots, causing my toe to hurt when hiking downhill and what's worse, making my big toenail turn black and fall off by the end of ice season! I have not noticed this kind of problem with the K4S and that's a really big plus.
I got a pair of K4S's to test starting at the end of the 2003/2004 ice season. I used them when I was guiding and to climb vertical ice several times and wore them in Huntington Ravine twice. Once was on an an exceptionally cold -5 degree day at Frankenstein, the others were in more typical spring conditions. I have also worn them a number of times in early ice season 2004, both in the ravines and on vertical ice and mixed ground on Canon & at Frankenstein. Although the lining on the K4S is the same as the Extreme, I found the K4S's to be a bit warmer than the Extremes. Since they have a synthetic lower half and a molded sole my foot seemed to stay drier, even in very slushy Spring and early winter conditions. My feet are generally warm, but it was nice not to have to break out the SuperGaitors on cold days. That said I would still probably use them when standing around with a group on Willey's Slide on a bitter January day!
Not surprisingly considering the components the K4S is somewhat more rigid than the Nepal Extreme, tho not as much as my trusty Expe's. Still it hikes reasonably well once I loosened the upper laces a bit. I really like the lacing system on the Extremes. All of the lower lace lugs on Extremes are rollers. In addition the lugs, where it turns to the ankle, have a cinch snap that holds the lace in place. Thus if the upper lace comes untied, not a totally uncommon occurrance, the entire boot won't almost come off. The K4S lower lugs aren't on rollers and pull a little differently. The upper lug is not a snap, but does cinch down, and I didn't find this quite as secure as that on the Extreme.
Although the soles are quite different, all of the crampons I tried fit exactly the same on the K4S and the Extreme. This made it easy to go back and forth between boots. On vertical ice the K4's performed very well. The snug heel cup remained firmly in place and the boot was stiff enough to provide the solid support that I'm used to. I felt totally comfortable standing on a single point on vertical ice or rock. On mixed ground with my monopoints there was just enough flex in the upper to allow me to bend my ankle when I needed to. Being a pound lighter made it easier for me to get my foot up in various positions as well.
I haven't had the opportunity to climb rock without crampons in the K4S. The Nepal Extreme has always been considered a pretty good rock shoe, in addition to everything else it does well. I have seen people climb things like Bombardment and Thin Air in Extremes. Comparing the edge of the sole of the K4S to that of the Extreme, I would imagine that the K4S wouldn't edge quite as well.
I found the K4S to be warmer and more comfortable than the Nepal Extreme. It climbs and hikes great, and performs well in all the conditions we threw at it. If you aren't sure that you will need to climb rock without crampons, the main advantage of the Extreme goes away. I haven't tried all the boots on the market, but this one is certainly is one of the best. If you're looking for a single boot, the K4S is a great choice and should be at the top of your list. I can only say that it's a good thing La Sportiva makes both the Nepal Extreme AND the K4S!
The K4S features a Benecke CeraCom® industrial fabric upper, PTFE/200g 3M Thinsulate™/3-bar knit inner layer and a insole combination of insulating honeycomb and carbon fiber. In addition it features the EZ Flex removable velcro adjustable tongue and EZ System lace hardware. The Vibram sole has a lug pattern that contains small pyramidal shaped lugs that are supposed to be provide better plunge-stepping and better heel braking.