How to Choose Alpine Ski Boots

Do you have doubts when choosing alpine ski boots? Race, All Mountain, Flex, rigidity, last, size, canting....this article will help you decide.

alpine ski boots, a key piece of equipment. Photo: Barrabes

What is an Alpine Ski Boot?

Although it may sound obvious, we will start by defining the type of boots we are going to talk about.

Skiers often use their touring ski boots for skiing on piste, but here, we’ll focus on the ski boots designed to work with alpine ski bindings (according to ISO 5335 standard).

There are some exceptions: until very not so long ago, no boots met both ISO 5335 (for alpine ski bindings) and ISO 9523 (for ski touring bindings). But today, many models comply with both ISOs, which is a great indication of what is to come in the future: an increasingly tenuous division between alpine and touring boots.

Compatibilities and Incompatibilities

One last clarification: regarding boots that feature the rubber outer sole system, ALL BOOTS AND BINDINGS THAT COMPLY WITH THE ISO 5335 STANDARD ARE COMPATIBLE WITH EACH OTHER, regardless of the brand.

But be careful! The latest ALPINE SKI BOOT DESIGNS HAVE A CURVED TOE AND RUBBER SOLE WITH A SIMILAR DESIGN TO THE TOURING BOOTS. These comply with ISO 9523 (touring), but incorporate a rigid plastic plate, (as required by ISO 5355), which allows them to perform like a downhill boot.

These boots do not comply with the ISO 5335 and are only compatible with alpine bindings specifically designed for these boots. These bindings are also compatible with classic alpine ski boots and are mainly used for freeride.

Complicated? You may want to read more about this in our article on The latest alpine ski boots: Is this an end to the compatibility of boots-bindings of different brands?, where we look at these alpine boots that do not comply with the ISO 5335, and the compatibilities between the different boots and bindings.

Alpine Ski Boots Today

The flex of ski boots has softened in recent years, and instead, boots have been reinforced laterally to adapt to a technique that emphasises greater lateral and less vertical movement. Few other changes in performance can be found in today's boots compared to those of a decade ago.

Clearly the most recent R&D investment prioritises versatility, comfort and customisation:

  • Custom fit shell and liner
  • Ski/Wallk mechanism
  • Greater sole grip
  • State of the art thermal insulated liners

They can be divided into the following categories:

1. Race Boots

Race boots renounce any advance that sacrifices performance in favour of comfort. However, brands have been advancing year after year to achieve greater comfort without sacrificing performance, thanks to custom molded shells and new materials with higher thermal capacity with no increase in weight or volume.

Everything to enhance your performance, with the comfort of other categories and the performance of a concept race boot.

Nordica Pro Machine 130
Nordica Pro Machine 130

2. Piste and All Mountain

Some brands, but not all, distinguish between their on-piste and all-mountain categories. However, there is very little difference between the two:

  • All Mountain offer the possibility of unlocking the cuff (not all) and non-slip soles.
  • On-Piste: Conventional plastic cuff and sole.
Salomon S/Pro 120 GW
Salomon S/Pro 120 GW

For Men and Women

Each category features specific boots for men and women.

Women's boots usually have the following features:

  • The cuff height is lower than on men's boots.
  • The last is wider.
  • The liners are lighter and more insulated.

In this article, Women’s technical mountain equipment: differences and benefits, we explain the reason for these differences, and many others.

Atomic Hawx Ultra 115 S W GW
Atomic Hawx Ultra 115 S W GW

How to Choose?

Our advice in this respect is clear. There are three main parameters to help you get the right boot:

  • 1. Flex index
  • 2. Size
  • 3. Last
  • Once you’ve narrowed down a selection based on these three points, if you then are able to choose something with a slightly more on-piste or All Mountain character according to your preferences, then all the better. But this is not the priority.

    Fundamental Criteria

    1. Flex index:

    The flex index refers to the level of resistance the boot provides when you bend your ankle forward.

    It is not standardised, so the recommended flex is a guideline.

    Your ski level and style, your height, and weight are the three factors that determine the amount of flex needed.

    For a typical skier (average build) it would look like this:

    (1) The difference in flex between a men or women's boot varies depending on the brand. Nordic differs by 15, so what is 130 for men is 115 for women, while Atomic and Salomon take it up to 30, so what is 120 for men is 90 for women. We think 20 is a good average.

    One last thing about flex: Never buy higher than your level. Being able to vary your centre of gravity by flexing your ankles is essential for your progression.

    If you are unsure, there are some models on the market that allow you to vary the flex by 10 or 20 points.

    2. Size

    Ski boots use Mondo Point sizing, which is the best system by far, as it indicates the centimetres of the foot... simple, effective, and universal.

    To know which Mondo Point size you need, just follow these steps:

    • Place your bare foot on a sheet of paper.
    • Mark the back of your heel on the paper and the end of your longest toe.
    • Measure the distance between the two points and round to the nearest whole number or half number.
    • If, for example, you get 24.13cm we will round up to 24 and that is the Mondo Point size.

    Full and half sizes usually share the same casing: in many cases the difference between a 27 MP and a 27.5 MP will not go beyond a thicker or thinner insole.

    The subleties of rounding up:

    • Skiers with narrow feet or those looking for maximum performance will ALWAYS round down: 24'13 cm will still be 24 MP but, 27'90 cm, which would normally round up to 28 MP, would round down to 27'5 MP.
    • If your foot is wide or if you have a high instep, you may find half a size larger is better for you.

    At our Barrabes stores your exact ski boot size can be calculated with the device below.

    Important! We do not recommend you choose the size based on your shoe size: in any shoe half or a one size larger is not usually a problem, and is normal when choosing sports shoes. However, a ski boot that is one size too large can be problematic and even cause injury.

    A poor fit makes the power transmission between your foot and the ski less efficient and this not only affects performance, but also reduces the binding’s capacity to effectively release the boot in a fall.

    Any reason (bunions, bulky calves, high instep, wide feet...) that in the past has led you to think that you had to buy a "larger" boot is wrong.

    A boot that is too long will cause the heel to move around and it is ESSENTIAL that it stays in a fixed position. Heel and toes first and then the rest.

    If you have any doubts regarding size, please contact our Barrabes store specialists or our call centre at

    3. Last

    Lasts are normally narrow, medium or wide.

    The boundaries of each are not clear, as they vary according to brand.

    But the 100 last (100mm wide) is generally referred to as the medium last. Anything above or below it will be wide or narrow respectively.

    To know the width of your foot, measure its widest part (from the first to the fifth metatarsal) but be careful with this as it can be confusing:

    • On the one hand, most brands only specify the last width of one size. A boot with a 100 last means that it measures 100 mm at its widest part in a men’s size 26'5 MP and a women's size 25'5 MP. This width will be wider in larger sizes and narrower in those that are smaller. And, unfortunately, the variation of the width from size to size is not provided by most brands.
    • On the other hand, the new heat moldable shells and liners always allow a margin of 2 to 6mm upwards depending on the model. It also depends on the area of the boot you want to expand, as not all areas can be deformed without endangering the structure and transmission of the boot.

    It is now possible to find almost all types of lasts in all ski boot types. With a few exceptions, such as Race boots which are only available in narrow lasts (98 mm is usually the width of Race boots that are not specifically for competition; for the latter, intended for professionals, 96 mm or smaller lasts are used), or the entry-level ranges for beginners and rentals which only offer wide lasts.

    Brands usually assume that a wide foot is associated with a wide heel and a calf of considerable volume, while a narrow last is associated to a narrow heel and smaller calf.

    However, this is not always the case and boots are unable to fit the shape and size of every foot or calf out there. This brings us to the next point: customisation.

    Customisation, Canting, Buckles, Liners and Heat Molded Shells

    Different technologies and mechanisms allow you to customise your boot to make it unique. There may be certain cases where customisation needs to be a little more radical and you will have no choice but to put yourself in the hands of an expert. At our Barrabes stores we offer alpine ski boot customisation at the time of purchase.

    The technician selects the boot that can be molded around your bunion, for example. That will be the starting point, where you begin to test and concentrate on the fundamental aspects of fit: heel positioning, instep support, flex index... even if the bunion bothers you; this will be the last step of the process. You can trust the technician: If you've been told it will fit, it will fit.

    The other option - the bad option - is to buy a boot three sizes larger.

    The custom fit systems are:

    • 1. Canting
    • 2. Forward lean angle and flex
    • 3. Macro-micrometric buckles
    • 4. Heat moldable shell and liner

    1. Canting

    Mechanically, by heat molding, or with a combination of both methods, the lateral angle of the cuff can be adjusted depending on your stance.

    If you suffer from severe pronation or supination, have bow or "X" legs you will probably have to adjust the canting.

    2. Forward Lean Angle and Flex

    Some boots allow you to mechanically adjust the forward lean cuff angle as well as the hardness of the flex. Both adjustments are a good idea if you are not entirely clear about your preferences.

    3. Macro-micrometric Buckles

    The ideal fit of a boot should be achievable without having to over-tighten the buckles.

    Think of the buckles as something that is there to keep the side flaps in place so that the boot doesn't open up when you put weight on it. If the shell and liner only feel as if they are hugging your foot after the buckles are fully tightened, the boot is probably too big. Either because the size or the last is too big, or both.

    Most boots on the market allow you to reposition both the buckles or tooth catches on the cuff to adapt to different calf sizes (macrometric adjustment).

    You can also finely tune the buckles by turning them (micrometric buckles).

    It is worth taking time to tune your micrometric buckles.

    4. Liners and Heat Molded Shells

    Most boots on the market can be heat molded. By heating the boot in a special oven, before putting your foot inside, the liner expands around the high pressure points to provide greater comfort and better power transmission from the skier to the ski.

    Basically, the higher the range, the greater the margin for customisation.

    Heat molding machines at Barrabes Barcelona
    Heat molding machines at Barrabes Barcelona

    Bear in mind however, that heat molding should be the second step, after having chosen a fairly good fitting boot. It is not intended for choosing a bad fitting boot and "remaking" the boot completely.

    On-line store:

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