Understanding the terminology used for the anatomy and functionality of a ski boot will allow you to be a better advocate for yourself in the ski boot purchasing process. Knowing what a ski boot can and can’t do will give you the confidence to make an educated purchase as well as improve your ability to use your ski equipment effectively.
The ski boot is the integral link between you and your ski. The movement and energy your body initiates is translated to the ski through the boot. Each component of a ski boot plays a specific role in both fit and performance. The key to a great day on the hill is a ski boot that fits well and performs to your needs.
SHELL The hard outer layer of the ski boot typically made of plastics. The shell provides the structure and stability to the boot. The shell consists of two parts, the lower shell and the upper cuff.
LOWER SHELL The lower shell is where your foot is contained. You want the shape of the lower shell to match the shape or anatomy of your foot as closely as possible for a great initial fit and one that will stay over time.
UPPER CUFF The upper cuff of a ski boot wraps around your shin, upper ankles and calf. It is usually connected to the lower shell by a hinge and can vary in height, stiffness, lateral stability and forward lean.
BOOT SOLE The boot sole, comprised of a toe and heel lug on the bottom of the boot, makes the primary connection between the boot and the ski. For safety and performance, it is critical to watch out for excessive wear. Walking on hard surfaces can damage the boots sole changing the interaction between the boot and the binding. Some ski boots have replaceable toe & heel lugs, but it is better to simply protect the soles of your boots by covering them or refraining from walking around in your boots.
BUCKLES The buckles (can be as many as 4 on each boot) are what close the ski boot securely around your foot and lower leg. The key components are the ladder or catch, the bail, and the buckle itself. The ladder or catch is the graduated rung that the bail, or wire, hooks onto so that the buckle can close to latch the boot securely.
INNER LINER The removable cushioned inner boot. The liner cushions and protects your foot from the outer shell. The materials used in the liner will vary by brand and by model and will have varying customization capabilities. The shape of the liner should mirror your foot shape, as well as the shell shape, for a good initial and long term fit. As the liner is key to transferring energy from the body to the ski, a good fit will enhance performance. Thermoformable foam liners use your foot’s heat to achieve a custom fit. The liners will break in and form to your foot after a day or so of skiing. Custom moldable liners use an artificial heat source to achieve a custom fit. This is best done at a ski shop with boot-fitting expertise.
POWER STRAP The power strap is a Velcro or mechanical strap around the top of the cuff of the boot and can act like a 5th buckle to securely and comfortably close the upper cuff around the lower leg.
FOOTBED or INSOLE The removable platform inside the liner of the boots on which the foot rests. Custom footbeds are those molded by a bootfitter to conform to the shape of the skier’s sole for better fit and more precise energy transfer.
NOTE: Most of the terms used below, from forward lean to last to flex are only relative within the brand. There is no industry standard therefore similarly marked models can vary significantly from one brand to the other.
MONDO POINT SIZING Most downhill ski boots use Mondo Point sizing, which is based on the length of your foot in centimeters.
BOOT SOLE LENGTH The boot sole length refers to the external length of the sole of the boot. This 3 digit millimeter (mm) number is usually marked on the side of the boot down by the heel. If you are demo’ing skis, they will ask for your boot sole length to adjust the bindings correctly.
LAST The Last refers to the interior shape of the ski boot. “Last” is a cobbler’s term for the foot-like form around which shoes were once crafted. Every brand has their “secret recipe” for building their “lasts”, which is why the fit can vary between ski boot brands.
LAST WIDTH The width of the inside of the ski boot at the ball of the foot. This measurement can range from 93mm to 106mm. Brands will provide many last width options within their offering. For example a 93mm last is a narrow lasted boot and will generally be more responsive for higher performance, while a 104mm last is wider and more comfort oriented. NOTE: this actual dimension changes with every size but only one number is shown as the average (usually based on the size 26.5).
FLEX Boots have a flex index number, which refers to the forward flexing stiffness of the boot – or how much resistance the upper cuff of the boot provides. The higher the number, the stiffer the boot, the more power transfers to your ski’s inside edge. The lower the number, the softer the flex, the more the boot will absorb impact and be easier to flex, but at the cost of performance. Generally, the flex index will roughly correlate to your ability level, but can also be influenced by your size and ankle flexion. Soft flex: Flex index below 80 Soft-flexing boots are typically best if you’re new to the sport or you’ve been at it for a while but enjoy skiing leisurely on groomed green and blue runs. A soft flex does make it a bit harder to control the ski; go a step up if you expect to progress quickly. Medium flex: Flex index range = 80 – 100 Medium-flex boots are geared to intermediate skiers and deliver increased responsiveness for improved turn-carving skills and higher speeds. They’re ideal for those who can comfortably ski blues and easier black runs and are ready to tackle steeper terrain, moguls and un-groomed snow. Stiff flex: Flex index above 100. Stiff-flex boots are highly responsive and generally offer greater sensitivity. They are designed for those who ski with confidence, speed and aggressiveness on the steepest and most challenging terrain. Note: Flex index ratings are comparable only within a manufacturer’s line. Also be aware that boots will have a softer flex at a warm indoor temperature than they will out on the ski hill – cold temperatures stiffen the plastic.
FLEX ADJUSTMENT Some ski boots have a mechanism where you can adjust the boots’ stiffness to balance comfort and performance or to match a particular type of skiing, like powder, groomers or bumps. A qualified boot fitter can also adjust the flex of a boot (permanently) by cutting (to make softer) or riveting (to make stiffer) the shell.
FORWARD LEAN ADJUSTMENT Simply explained, the forward lean of a boot is the amount the boot forces your ankle to bend when you are standing in it. Boots equipped with a forward lean adjustment can be fine-tuned to your own neutral athletic stance, where your knees and ankles are bent and your weight is primarily on the balls of your feet but evenly balanced from side to side so you are ready to respond quickly and move in any direction. One can also use spoilers to adjust the forward lean or, in the case of Tecnica’s women’s boots, utilize the C.A.S. Thermoformable Cuff to alter the forward lean.
CUFF ALIGNMENT The cuff alignment adjustment allows the upper cuff to move laterally in or out to match the angle of the lower leg. This adjustment is helpful for those that are bowlegged or knock-kneed to achieve a comfortable and balanced stance within their boots.
CANTING Not to be confused with cuff alignment, canting changes the lateral angle of the sole of the boot. Boots can be canted inward or outward, usually by grinding the sole at an angle or with the use of shims, to allow your skis or your feet to rest perfectly flat on the ground and give a skier better access to all four ski edges.
SKI/WALK A feature that allows the upper cuff to move more freely when released for easier walking or hiking / skinning into the backcountry. You lock the cuff back into place when skiing.
RAMP ANGLE This is the angle between your heel and the ball of your foot in relation to the ski. This angle is created primarily by the boot and on some boots may be adjusted to shift your center of mass either forward or backward in order to maintain a neutral athletic stance with the weight balanced on the balls of the feet while still allowing for the use of the entire foot to apply pressure to the ski.