Demystifying how ski boots work

Breaking down the nitty gritty on ski boot anatomy.

We know, we know… bootfitting seems outright complicated. And it is. If you’ve ever wondered why they’re so awkward to walk in, why there’s a specific order to follow when buckling up, or why some people experience pain in their boots while others have none, you’ve come to the right place. Our team at Pulse is a bank of knowledge — at your disposal.

By examining each part of the boot, we can understand how each function cohesively works together to maximize your skiing experience.




We’ll start from the outside and work our way in. The shell refers to the hard plastic exterior — typically made from polyurethane (or PU for short), or a polyamide, such as Grilimid — of the boot. It’s made of two parts: the lower shell, or clog, and the cuff. The lower shell contains your foot while the cuff is the section that encases your shins and lower leg. The shell determines most of the shape and performance of the ski boot. Expect a bootfitter to compare the shape of the shell to your foot and try to find a snug match that will ensure your foot is evenly held and supported, while offering a flex that complements your anatomy and ski style. They may also stretch or grind your shell to expand it if necessary.


Psst: Speaking of shells, you may be wondering what the term flex means. Flex is another word for stiffness — it’s a measurement of how stiff a boot is. The scale of low flex (meaning very soft) to high flex (meaning very stiff) tends to be difficult to measure, since there is variation among boot manufacturers. That’s where the bootfitters come in handy, since they know manufacturer differences well and can get you set up with the flex you’re looking for. Some boots even offer flex adjustments by using the bolt at the back of the boot. While ski boots are relatively easy to soften, Pulse Boot Labs have developed a product called the Proflex, which is one of few ways to stiffen a ski boot.


Forward lean refers to the tilt of the ski boots, which pitches your lower leg forward so that your knees and ankles are bent. This can be adjusted as far as 17 degrees, and explains why walking in ski boots can be quite the task.


Ramp Angle refers to how your foot sits in relation to the bottom of the boot. Your heel is always a little higher than your toes, and the angle of this affects how you are balanced over your skis. The combination of ramp angle and forward lean is called your delta and affects how bent your ankle is in the boot and how much range of motion it has as well as how your foot and leg are positioned.



The footbed, which sits underneath your foot, is your foundation. It needs to support your heel and ankle in a centred position to prevent your foot from moving into the sides or front of the boot. It also gives your feet more surface area to feel feedback from the skis and boots. For maximum performance and comfort, we usually always recommend replacing the footbeds that come with new boots with a custom insole tailored to your specific needs.



The liner fills the space between the foot and the shell. It provides padding, support, and warmth. Stock liners are a generic shape which needs to both fit many different feet and feel comfortable enough for people to want to buy them out of the box. Different custom liner options are out there. Thermomoldable liners are designed to be heated up and put on a foot so the material compresses to the space available to better support the foot. Injected liners are the premium option, where they are filled with expanding foam to exactly the shape of the foot and shell. These have the most support, last the longest, and give the best performance and feel when skiing.



Buckles are the latches that determine tightness and prevent your boot from opening.  These are the most common closure system for boots. The length of the buckles can typically be adjusted by rotating them prior to latching, allowing for micro adjustments. Having to close buckles tightly can be an indication that you are in boots that are too big or your liners are wearing out.



Often referred to as powerstraps, these are Velcro or camming straps near the top of the boot used to tighten the top of the boot to your leg. This helps transfer energy from the lower leg through the spine of the boot, where most of the boot’s strength is.


Rear Spoiler

This one is optional, but rear spoilers are plates situated between the liner and the shell that push you slightly forward in your boot, thus increasing the forward lean. These are great tools for those with slender legs who want to customize their boot fit even further.


Seal Toe Dam

This rubber piece sits at the bottom of the split in the lower shell and keeps snow and water from entering the boot.


Cuff Pivots

Cuff pivots are the side attachments between the upper and lower parts of the shell. These may have an adjustment to change cuff alignment. In touring or hybrid boots, cuff pivots may use Teflon or another material to reduce friction when the cuff rotates around these pivots in walk mode.


Walk Mechanism / Cuff Bolts

Where the spine of the upper and lower parts of the shell connect. Most of the stiffness in an overlap boot comes through the spine, so the stronger the connection here, the stiffer the boot it and the more rebound it has. This is difficult to achieve effectively with a walk mode, which is why hybrid and touring boots have consistently softer flexes and less rebound.


Replaceable Toe and Heel Sections Outsoles

These are the bottom of the boots. Nowadays, there are three different standard dimensions, which affect which bindings will work with which boots. Gripwalk is now the most prevalent, and most modern bindings work with it. Outsoles used to be hard plastic, but in recent years, rubber is becoming more popular to give better grip when walking. These are often replaceable as they are one of the fastest wearing areas of a boot. Especially when walking in parking lots and on pavement. Race boots generally don’t come with replaceable soles, but it’s common to add ‘lifters’ which raise the height of the boot and can be replaced when worn out.


Toe / Heel Lugs

Toe and heel lugs are the ledges on the toe and heel that a binding clamps onto. In hybrid and touring boots these usually have inserts to accept pin bindings for touring. When lifters are added to race boots, or canting is used to change the sole angle, a bootfitter will need to router the lugs so they interface properly with bindings.


Boot Board

Sitting inside the bottom of a shell, the boot board (or zeppa) ensures a flat surface for the liner and footbed to sit on. Before custom insoles became as prolific as today some boots had a small amount of heel or arch support built into them that bootfitters had to grind flat when adding footbeds. Boot boards may be rubber or plastic depending on the priority of cushioning and shock absorption or power transfer.

Back to blog