K4S Mountaineering Boot

Very pleased with this boot.
It's at least as warm as my old invernos yet hikes and flatfoots like my makalus and ice climbs better than both yet weighs less than either.

Very supportive with plenty of stiffness to frontpoint all day, yet enough ankle flex to drive comfortably. Edges on rock like a leather single boot. One note though, it uses the same last as the makalu, and i've found that the footbox is slightly more forgiving. Dozens of miles and and long weekends has not given me any unpleaseant suprises with break in. They don't freeze solid overnight like leather but will become stiff as the insides predictably freeze and stiffen the boot temporarily. This has cleared up must faster than my experiences with frozen leathers.

So far spent a day on mid minus 20 celcius weather in them with no problem, and if they keep up with even colder weather I will never use plastic boots ever again.

update: After yet another season, these boots have come though for me time and again. wether it's hiking flats for over 17 miles in summer, climbing 5.5, overnights at -15C or sustained step kicking in 40 degree snow, it has consistantly exceeded my expectations in almost every respect, with one exception.

Crampon fit is a problem with step-ins. 2001 Model sabertooths have been solid, but rambos and rambocomps have given me much trouble with the heel bail popping out of the crampon due to the unusual width of this warm boot and the height ot the heel welt. This was for a size 43. This has been a major irritiant for ice climbing and it is imperative that you test any new or existing crampons for fit on this unusually wide boot.

update: Summer trips in scree have started to degrade the stitching on the inside outer boot between the heel and the ball of the foot. A layer of seam-grip on the exposed stitching has solved this, but would recommend this be done to new boots as a preventitive measure.

I am glad to get these boots for climbing on the snow/ice. They are light, warm (I am having cold feet even here in Sierra's spring) and waterproof (whaty do you expect from the plastics). On the other hand they are flexible enough to make you walking in comfort on the snowless trail. I got some blisters, but I never expect to "brake" any brand new boots without having problems. Overall - highly recommended.

I owned a pair of the K4's and finally sold them after about a year. Personally I think they are bit overrated. The positives are it is a warm boot and the materials used are waterproof and being manufactured by La Sportiva it's impeccable workmanship. The uppers are also very flexible.

Having said that, there are, IMO, two design flaws with this boot. First, the boots have no rocker sole. Because it's stiff (and meant to be), it makes it less efficient for approach, without a rocker sole. You'll notice an immediate difference if you compare it to a stiff boot with a rocker sole. The best stiff boots out there are designed with a rocker sole. Second, I found the binding system for crampons to be rather poor in design. The groove at the front of the boot is somewhat narrow making the crampon bale sometimes difficult to fit into and the ribbing material on the back of the heel keep the crampons from snapping shut with a 'whack'. I tried Grivel's and the new BD sabretooths that did not work, at least for me. The only step in crampon that would work was my old BD sabretooths. If you plan on getting this boot, make sure your crampons fit.

Also of note, La Sportiva appears to have stopped manufacturing this boot. Probably because they have it's function covered thru either the Nuptse or Nepal Evo. Speaking of the Nepal Evo, I personally found the Nepal Evo to be a much better boot (for me) in both comfort and performance when compared to the K4.

Got a pair for Christmas last year. Great for ice climbing but I did get some blisters while mountaineering. These boots are still in their break-in period so blisters are to be expected and being proactive has kept them from coming back. With the removable adjustable tongue you can give them a custom fit. I now find them to be very comfortable on the trail, glacier or vertical ice. I would highly recommend this boot if it was still being made.