In recent years, as backcountry skiing has taken off, equipment has steadily improved. Thirty years ago "AT boots" were either glorified ice climbing boots, or alpine race boots with a rubber sole. By 15 years ago there were a handful of rudimentary products one could choose from. These foundational AT ski boots aimed for a perfect balance of uphill and downhill performance, without excelling at either. The past decade has seen a rapid increase in the quality and quantity of options. Progress has occurred in three main directions, with boots falling into three corresponding categories.
The Types of AT Ski Boots Available
All Around AT Ski Boots
Boots we term as "All Around" are manufacturer's attempts to optimize a nearly equal balance of uphill and downhill attributes. The boots in this category have improved in recent years in both ways. They tour better *and* ski better than their predecessors. In most cases, the improvements are significant and result in boots that serve a wide range of users.
Middle ground AT ski boots differentiate for consumers mainly on fit differences, though they also vary some in performance, weight, and slight differences in the relative optimization of the uphill/downhill balance. It must be acknowledged that brand loyalty and other marketing pressures may play into your choice. There are tons and tons of excellent options in this category.
Identify All Around AT ski boots as those with a weight between 5.5 and 7 pounds (per pair) and 2-4 buckles plus a "power strap".
Super-light AT Ski Boots
Borrowing technology, materials, and design cues from randonnee racing or "SkiMo" racing boots (which we do not discuss nor review here, as they are very very specific in function), the lightest and most flexible end of the AT boot spectrum is the most exciting, recent, and fastest innovating subsection of this market. In balancing the uphill and downhill performance attributes, the designers of these boots lean hard to the uphill end of the spectrum. In some cases they climb and walk as well as winter mountaineering boots, while providing the technically proficient skier enough support for all but the most "high energy" downhill techniques. The best boots in this category ski almost as well as your normal touring boots, with a weight and cuff range of motion that allows touring freedom for huge days and minimal energy expenditure.
Identify Super Light AT ski boots with a weight under 5.5 pounds (in some cases, as low as 3.5-4 pounds), 1-3 buckles, and a cuff range of motion greater than 40 degrees.
Alpine Ski Boots with Touring Features
The final category of AT boots is those that are essentially resort, all-mountain alpine ski boots with a rubber sole, ski/walk mode switch, and metal fittings to work with modern "tech style" AT bindings. These boots ski downhill really well, with stiffness and responsiveness that simulates that of dedicated inbounds boots. Their uphill performance and features are rudimentary at best, as it still proves difficult to optimize for both up and downhill. The best boots in this subcategory ski basically as well as your all mountain alpine boots, and tour almost as well as an average all around AT boot.
Identify touring featured alpine boots by their "overlap" shell construction, weight over 7 pounds per pair, and compatibility with both tech and DIN AT bindings.
How to Choose AT Ski Boots
Choose Your Category
Your first step in choosing AT Ski boots is to decide on which of the three above categories you are looking at. Most people will choose a boot from the all-around list. You likely already have a resort alpine set-up, and are looking for boots for dedicated backcountry missions. These backcountry missions may range from short "out of bounds" excursions to serious ski mountaineering expeditions, but the equipment available in the all around category will serve all these purposes.
If you are very apprehensive about the downhill performance of your backcountry gear, either because you ski very fast and hard or because your backcountry ski technique is still in its early stages (backcountry ski technique starts with expert level in-bounds technique. Beginner or intermediate resort skiers need more time, training, and skill from the resort before venturing onto the wild snow of the backcountry. Even for expert level resort skiers, backcountry snow is difficult), the slightly modified alpine boot selections are likely most appropriate. These heavier and ski-optimized AT boots are also worth considering for the dedicated backcountry skier that wants a second set up for occasional resort use or shorter days of human powered skiing.
For those backcountry skiers that have some mileage under their belts and may already have an all-around set up, a lightweight boot is worth considering. It will be a rare case in which a backcountry skier buys his or her first AT boots in this ultralight category. This rarity is increasing in likelihood as the lightweight boots improve in comfort and downhill performance and exactly what they are capable of is is being demystified by more and more use.
Fit and Comfort
After narrowing down the category in which you will be shopping, you must consider fit. Fit is king. Boots that are uncomfortable will ruin your day, week, trip, or expedition. They may even damage your feet and adversely affect your perception of all of backcountry skiing. In each major category of AT ski boots there are now multiple options for feet of different shape and size. In shopping for AT boots, consider giving yourself a little more room than in your regular alpine boots. Touring and warmth both benefit from having a little more space.
Like with alpine ski boots, AT boots are sized first by length. The "mondo point" sizing system is a simplified foot sizing metric that is basically a measure of the length inside the shell, in centimeters. The "catch" is that so-called half sizes, across all brands, are the same shell size as an adjacent whole number sized shell. In most brands, the size 27 boot has the same shell as the size 27.5 boot. This allows the manufacturer to offer half sizes of boots, while only making expensive molds for every other boot. How the manufacturers make the half size boot actually a different size is a bit of a mystery. Some claim to use a different liner, some ship the boot with a different thickness of "insole" (which most users dispose of immediately anyway), while others may mold the liners with more space in the bigger labeled boot. It is conceivable that there is no actual difference in the half size boots from some manufacturers. Finally, further confusing things, while most manufacturers make the half size boot in the same shell of the next size down (as in the 27 and 27.5 example above), others make the half size boot the same shell as the next size up. In this case, the 27.5 is the same as the 28. Wicked confusing. Be patient, do your research, and whenever possible, try things on.
After length, you need to consider the "volume" of your particular foot when choosing boots. Some feet are lower volume, or narrower, while others are higher volume. Each boot model comes from the factory with a volume pre set for a certain sort of fit. This volume is essentially fixed for a given model of boot. Your feet are a flexible matrix of bone, muscle, and connective tissue. In skiing and touring, they move, flex, and swell in all dimensions. They should be thought of as three-dimensional, semi-fluid shapes. It is the volume of the boot and the volume of your feet that need to match. Actual volume of a ski boot is very difficult to measure, and is therefore not reported. Try things on and use our reviews for comparative assessment of the relative volume of different boots.
Manufacturers report on the "last width" of their boots. This is an attempt to quantify the width of the boot. However, it is the width of just one spot in the boot and is measured, in most cases, on a "slight diagonal". Specifically, last width is supposed to be measured inside the shell of the boot, across and parallel to the rough location of the metatarsal heads. The metatarsal heads are the joints at the base of each toe. The line of the last width traces the line that connects these 5 joints. With anatomical differences and different manufacturer's interpretation of a line parallel to these joints, on company's 100mm last can feel the same as another's 104mm. In alpine boots, where company's often manufacture the same model in 2-3 different last widths, these numbers are useful. For comparing boots between different manufacturers, they are basically irrelevant. AT boot models, except for rare exceptions, are made in just one last width. Nonetheless, AT boot manufacturers report on their last widths, and many consumers, conditioned by their shopping in the regular alpine boot market, hone in on these numbers as the gospel truth. Buyer beware of the value of these numbers.
Every AT boot on the market has a liner that can be heat molded. For the careful shopper with anything but the most dramatic of foot issues, liner molding is all that is necessary to fully accommodate your feet. Some liners, especially those in the ultralight boots, are quite thin. These thin liners have less "room" for molding customization and less material for padding tough-to-fit spots. Shell fit is very important in the ultralight boots.
Finally, most boots can be adjusted, slightly, in terms of shell fit. Some materials are easier to work with and some are impossible to adjust. Carbon fiber is light and stiff, but cannot be adjusted at all. Grilamid is light and stiff, though less so than carbon fiber. Grilamid can be altered, but it is very difficult. Pebax is common, inexpensive, and not as stiff as grilamid. It can be worked with, but it is also difficult. Polyurethane is the least expensive material used in boots and is easy to work with for fitting. If you have dramatic fit issues, polyurethane is likely your best choice, but it must be noted that its stiffness is less than the other options and its stiffness is vulnerable to temperature changes. Lastly, some boots are made of proprietary plastics that are very very easy to manipulate. In our review, the Fischer Transalp Vacuum TS is made with a plastic shell material that can be heat molded not very differently than liners can.
Warmth and Insulation
AT ski boots will be used in cold climates. In the case of multi-day and expedition backcountry skiing and ski mountaineering, the insulation value of your boots can have survival implications. With a wide range of ski boot thicknesses now available, the insulation value is an important consideration. It used to be that all AT boots insulated similarly. Now, the lightest ski boots aren't much more insulating than hiking boots, and your usage and selection has to take this into consideration. Basically, there is a fairly direct relationship between ski boots' weight and their warmth. Heavier boots that are thicker are warmer. After that, fit affects warmth. Close fitting boots inhibit circulation and compromise insulation value. For expedition, multi-day, and very cold climate day-trip use we recommend sizing up a full shell size and installing a thicker liner.
What used to be a major question is now becoming fairly standardized. For all human powered backcountry skiing, "tech" style bindings are most appropriate. There are other systems available, but these are far inferior to the current "tech" standard. We mention it here and in our review only because some consumers are conditioned to consider their options.
Special mention must be made of AT boots made for both tech style bindings and a new resort binding format called WTR (short for "Walk-To-Ride"). In our test, the Lange XT FreeTour 130 can be used with both tech bindings and with these WTR bindings.
After you have decided your main category of boots, found an appropriate fit, and assessed your insulation needs, any remaining variables are very very minor. Within a given sub-category, durability is fairly consistent. Lighter boots are less rugged than the beefier ones, but boots of similar weight aren't that different in terms of durability. There are small features like climbing features, crampon compatibility, ease of transitioning, and versatility that may play into your ultimate choice. If you are making choices that nuanced, however, you are likely a savvy enough consumer to sort out those differences on your own. Just be careful that those small details aren't getting in the way of the big, major questions you need to address first. If your boots aren't warm enough or don't fit well or don't ski well enough for your needs, the availability of swapped soles or step in crampon compatibility won't make a huge difference. Ask the big questions first, and let the rest fall into place.
Where are you going to use these boots?
Fit is certainly one of the most important factors when considering which AT boot to buy. The first thing to consider is that your touring boots should not be as tight as your alpine boots. If your toes are continuously pressing against the front of the boot, you'll likely loose some toenails during a long flat skin. You're also likely to spend a lot more time during the day (or multiple days) in your touring boots than your alpine boots. Most alpine touring boots feature thermo-moldable liners, because they are warmer and lighter and help produce a better fit. Getting a proper boot shell fit is key, that way you know (at least lengthwise) that the boot should work for you.
Most Alpine touring boots come with thermo-moldable liners meaning that the liners change when you heat them up to better fit your foot. Getting them heat-molded is certainly something you want to have done by someone who has done it before. It does make a pretty significant difference.
Mondo sizing was an attempt to be the end-all of boot sizing discrepancy. Yet like all other units of measuring peoples feet, it is relative. The number was supposed to be a length in centimeters of the users' foot.
Many boots label their production last width, which is the diagonal distance across the widest part of your forefoot, measured just slightly behind your toes. The given last width is for a particular model in a size 26.5 boot. Take, for example, a boot that has "101 mm" last width. That number is what you could measure in a size 26.5. Size 30 might then have a 107 mm last width. Alpine boots seem to average 98-100mm in last width. Around 101-104 mm is a pretty common in AT boots because of the idea that users will be wearing them longer and are willing to sacrifice a little performance for all-day comfort. In our experience testing many boots over years and years, last width is useful information, but only part of the story. The reported width is an attempt to standardize comparisons, but there are still many, many variables that are not contained in that number. Always, it is best to try on your potential boots. In our reporting, we attempted to make generalizations based on actual feet-in-boots, head-to-head testing, with a variety of users. We are confident that our relative reports of actual sensory experiences are more valuable than the snapshot provided by a last width number.
Boot Shell Materials
Alpine touring boots are made from a variety of plastics and carbon fiber. Often randonee boots use a higher quality plastic than downhill boots that is stiffer for its weight. Generally speaking the more you spend, the nicer the materials. Some common boot shell materials are Carbon Fiber, Grilamid, PU and PX.
As you would likely guess, this is the lightest and stiffest material used in touring boots. It is minimally affected by cold but is nowhere near as durable, nor as moldable for fit issues, as most plastics. For these reasons, most boots simply use it in the cuff and not the lower shell. Exceptions include super-lightweight ski mountaineering and rando racing boots. Lastly, carbon fiber makes everything cost more. Similar to carbon fiber, but less expensive, is a sort of proprietary fiber glass that some manufacturers use. Notably, the Editors Choice Dynafit TLT 7 uses a woven, laminated cuff material that isn't carbon fiber. It is a little less stiff than carbon, but also less expensive. It has similar durability and moldability issues as carbon.
Of the plastics currently in widespread use, Grilamid is the stiffest for its weight. It is also the most expensive plastic. It is harder for boot fitters to work with Grilamid than with the other plastic options. Unlike Polyurethane and similar to Pebax, it presents almost no change in stiffness with temperature.
Pebax or PX:
Not to be confused with the base material P-tex, PX is likely the most popular shell material among randonee boots. It isn't as expensive as Grilamid but it is more expensive than polyurethane. Pebax is stiffer for its weight than PU and offers the desirable characteristic of a more consistent flex regardless of temperature. Pebax is harder to have a boot fitter work with than PU because of its strong "memory", but it is still possible. Lastly, most users feel PX is more "reactive" than PU, but as a result, slightly less damp.
Polyurethane or PU:
Stiffness of polyurethane is dramatically affected by temperature. As it gets colder, polyurethane gets stiffer, but on warmer days it is softer. For those who need a lot of boot fitting work done, Polyurethane is the boot material most easily manipulated.
Tech Binding Compatibility
We only considered AT boots with steel toe and heel "tech binding" fittings in them. In fact, at this point in history, it would be hard for us to call a boot a backcountry ski boot if it didn't feature tech fittings. With even the large alpine binding manufacturers making and selling tech bindings, touring with "frame style" bindings is a thing of the past. Only the absolute biggest backcountry cliff drops and the most high-speed skiing maxes out the performance of tech bindings. If you truly need more than tech bindings provide, you are in the upper 1%. We speak here to the vast, and growing, majority of users for whom tech bindings (and therefore appropriate boots) are the best choice. We do all of our backcountry ski and boot testing on tech bindings.
The boots with interchangeable soles in our test (the Lange and Tecnica boots) are also the best skiing boots and the heaviest. The soles are interchangeable so that, as the sole rubber wears down, it can be replaced for use in AT "frame bindings". Unlike swap-sole boots of the past, these models cannot be used in standard alpine bindings! The Lange, however, can be used in special alpine bindings. The WTR binding/boot interface ("Walk-to-Ride") offers the security and reliability of alpine bindings, with walking comfort and traction that approaches that of regular AT boots. The Lange soles are slipperier than others, but the versatility is welcome.
Don't use your AT boots in your alpine bindings!
As tempting as it might be, don't put any rockered touring sole ski boots into DIN/ISO 5355 alpine bindings (typical alpine bindings). They may, or may not fit, but the release value likely won't be consistent and your odds of injury are much higher.
Other important considerations when purchasing an Randonee boot.
Can I just tour in my downhill boots?
Most downhill boots will fit into most frame style bindings like the Marker Duke, Barron and Fritschi Freeride. This is a reasonable introductory strategy, but not ideal in the long term. Touring in alpine boots with little-to-no walk mode is much harder on the uphill and just straight up, less comfortable. Most people who try to do it for any kind of extended tour will end up with shredded and sore shins. Additionally, these bindings suited to alpine boots are much heavier, less reliable, and becoming less and less available as tech bindings improve and reach more users.
Uphill Performance vs. Downhill Performance
While certainly far from universally true, to some extent, lightweight, more comfortable fitting boots don't perform as well on the descent as their more heavily laden counterparts. You can't have it all. The attributes that make a boot ski downhill well inherently limit uphill performance, and vice versa. Lightweight boots with great cuff range of motion and low friction in tour mode climb best. Boots with thick shells, secure buckles, tight rivets and manufacturing tolerances, and close fit ski downhill best. Of course, the entire AT boot category exists to balance these attributes. We tested products from across the spectrum, and have done so for years and years now. As time goes by, and technology improves, we find that the compromises are less and less. The best touring boots ski better than you could ever imagine 10 years ago. The burliest downhill performers are comfy and usable for light to moderate pace and scale of uphill efforts. Our Editors Choice winners are especially well-tuned for optimal downhill/uphill balance. The TLT 7 tours almost like a randonnee race boot and skis downhill like your average ski touring boot. The Salomon Mtn Lab skis almost like an alpine boot and tours like your average ski touring boot. Take your pick, consider fit, and one of these is apt to blow your mind in terms of optimal compromised performance.