Frequently Asked Questions

zUFO, the modular, eco-designed and comfortable ski boot!


How to choose your ski boots?

The main criteria to take into account when choosing your ski boot are:

For comfort:

  • The size of the foot,
  • The morphology of the lower leg,
  • The ergonomics of shoe / shoe removal, options type “on position”,
  • Lightness,
  • The precision of the clamping system.

For performance:

  • Flex / rigidity,
  • Angular travel in the disengaged position (for hiking shoes).

For the type of practice:

“Classic” ski boots are classified as follows, ranging from the heaviest and stiffest to the lightest and most flexible: piste // freeride (off-piste) // freerando // hiking.

Concretely, how are these criteria managed?

For “classic” ski boots:

  • If it is easy to find a shoe at the size (length) of your foot, it is more difficult to find a shoe adapted to your morphology (in particular width at the metatarsals, ankle and calf as well as height at the level of the kick). See more details in questions related to morphology.
  • Conventional shoe manufacturers provide an index of Flex. The higher the index, the stiffer the shoe. See more details in questions related to flex.
  • Manufacturers have a dedicated commercial offer per type of practice (track / freeride (off-piste) / freerando / hiking). Some models are more versatile by covering two types of practice. This is done at the expense of performance for each practice.

For zUFO ski boots:

zUFO, thanks to its patented technology “without rigid shells” and its independent management of mechanical functions on one side and thermal insulation + waterproofing on the other allows to adapt to all morphologies.

Its Flex is mastered and depends only on one part. So by adjusting this piece or replacing it you can choose the Flex you want according to your level and your ski practice.

In addition, zUFO is designed to perform well for ski touring (lightness, detachability, high angular travel). However, zUFO’s patented technology without a plastic shell provides a rigidity that allows you to practice skiing on the slopes in a comfortable and efficient way.

Finally, zUFO is an eco-designed ski boot. Its life cycle is optimized by its modularity and its materials are chosen according to their technical and environmental performance.

Which ski boot to choose to be adapted to your morphology?

First of all, it is necessary to specify the main parameters of the morphology of the lower leg :

  • The size (length) of the foot
  • The width of the foot (at the metatarsals) (4)
  • The height of the kick (related to astragalus) (3)
  • Ankle width (2)
  • Calf width (1)

With “classic” ski boots you can opt for a width adapted to your foot (manufacturers provide, for medium / high-end boots, three different widths for a given foot length). The width at the ankle and for the calves is usually fixed. The height at the astragalus / kick too. The adjustment of the tightening of the hooks makes it possible to tighten more or less but does not allow to modify the shape of the shell to its convenience. And in any case, the technology of rigid plastic shells does not allow to choose combinations of width such as: wide foot to metatarsals / strong kick / thin ankle / strong calf.

In order to best adapt your shoes, you can call on “boot-fitting” specialists who will play on the deformation properties of the plastic by heating it. It is necessary to be accompanied by a good specialist to guarantee an improvement in comfort.

Excluding “classic” technology, zUFO, with its patented technology “without rigid shell” and its independent management of mechanical functions on one side and thermal insulation + waterproofing on the other allows to adapt to all morphologies:

  • The foot rests on a rigid sole and is held in its drop (level of the metatarsals) and its height (level of the astragalus / foot cut) by a flexible but firm envelope that naturally adapts to each morphology,
  • The ankle is not in contact with the structure of the shoe,
  • The calf is held by a headband that adapts perfectly to the width of all calves while providing effective control (Flex + square grip).

Are there eco-friendly ski boots?

As in other areas, ski boot manufacturers are becoming aware of the impacts of the industry and the practice of our sport on the climate and our environment.

Some brands include recycled or biobased materials in their production, others launch recycling programs. These initiatives are a first step. We hope they will continue to evolve towards a more comprehensive approach

Since its creation, zUFO has wanted to integrate a systemic vision and include the entire life cycle of the ski boots (from the origins of raw materials to its end of life) at the heart of its development.

To carry out this work, we have teamed up with external skills specialized in eco-design in order to set up a methodology adapted to our product, its industry and its use.

This methodology was awarded by the Perfecto national call for projects from ADEME for a product that reduces the environmental impact according to 4 areas of work:

– Reduction of Segmentation (versatile and efficient ski boots)

– Repairability + Recyclability (thanks to the modularity of the exoskeleton)

– Short Circuits (locally manufactured modules)

Product Service System (sale / rental / subscriptions)

A real pride for us and also recognition of the work already done.

At zUFO, we created an exoskeleton ski boots concept from scratch. It is naturally that our ski boots were born eco-designed.

We are supported by an eco-design agency Agence Think+ which helps us to make the best possible environmental choices by taking into account tangible criteria : technical, economic and environmental.

Being awarded commits us to this eco-design approach and for future communication relating to our environmental approach, which will be carried out according to the ISO 14021 standard (“anti Greenwashing”).

How much do ski boots weigh?

With the classic technology of ski boots, it is the plastic shell that creates the structure of the boot. The more we increase the thickness of the hull, the more rigid this structure is, the more control there is but… the heavier the shoe.

For this reason, we will have heavier boots for the practice of downhill skiing than for other practices because we favor performance rather than weight.

On the other hand, we will look for lightness for hiking practices for example, the Practice Freeride and Freerando being in between.

Here is a table summarizing the weights of ski boots for each practice:

Skiing Weight of a shoe (x2 for the pair)
Downhill skiing 1.5 to 2.5 kg
Freeride Skiing 1.5 to 2.2 kg
Ski Freerando 1.4 to 1.9 kg
Ski touring 1.0 to 1.4 kg

Note: weights are usually given for a size 27 (mondopoint) or 42 (Europe).

Regarding zUFO, at the time of writing (03/2022) we are in the R&D phase. The choice of materials is not yet final for all our components and the optimization of the sizing of the components is not yet realized. Our goal is a shoe with the weight of hiking shoes (1 to 1.4 kg).

What is the Flex of a ski boot?

The Flex is an index that characterizes the rigidity of a ski boot.

With the technology of “classic” ski boots it is necessary to find a compromise between comfort and control : The more flexible the boot, the more comfortable it is (the plastic shell whose shapes do not necessarily correspond to the morphology of the skier will be more malleable), the more rigid it is the less it will be subject to uncontrolled deformations that handicap control and performance.

To characterize this rigidity, manufacturers of “classic” ski boots have invented the Flex index. This index is not standardized. It follows from the judgment of each manufacturer and is not based on any tangible data. This implies that two shoes from separate manufacturers with the “same” Flex do not necessarily have the same rigidity (which the Flex is supposed to characterize).

In addition, for a given shoe, the rigidity will not be the same depending on the tightening of the hooks (tighter hooks = stiffer shoe), the outside temperature (the plastic is more malleable when the temperature rises) etc …

For the anecdote, some ski competitors bury their boots before World Cup starts to cool the plastic shell and make it stiffer! It should also be noted in passing that at the arrival of the competitions, the first reflex of the majority of skiers is to open their hooks …

What to remember for the Flex with “classic” ski boots:

  • Choose a low Flex (80-100) if you want to favor comfort and a high Flex (120-150) if you want to favor control,
  • The Flex is an index that is not standardized and depends on subjective judgment. For a given shoe the rigidity will evolve according to many parameters (tightening of the hooks, outside temperature …) and the rigidity, therefore the behavior of the shoe, evolves over the course of a day,
  • Two shoes of different brands with the same flex declared will not necessarily have the same characteristics.

And with zUFO?

We consider that the ski boot should be considered as a mechanical object, in the sense that its main function is to transmit the efforts between the body and the ski (in both directions).

For this reason, we have made the mechanical function of the ski boot independent of the other functions it must perform (thermal insulation and waterproofing), according to patented technology.

The mechanical behavior of zUFO depends only on one part that can be adjusted or replaced by another part according to its skiing practice and the transmission characteristics of the body / ski forces that one wants to obtain.

The “Flex” or rather the mechanical behavior of zUFO will be measurable in a tangible way and will not depend on external parameters (it will therefore remain constant).

What is the size chart of ski boots?

Here is the conversion table that gives the equivalences of ski boot sizes according to the country:

27 9 10
28 10 11
29 11 12
30 11½ 12½
31 12½ 13
32 13½ 1
33 1
34 3 2⁄3
34.5 2 3 4
35 215
35.5 3 4 5 220
36 225
36.5 3 2⁄3 4 2⁄3 5 2⁄3
37 4 5 6 230
37.5 235
38 5 6 7 240
38.5 5 1⁄3 6 1⁄3 7 1⁄3
39 245
39.5 6 7 8 250
40 255
40.5 6 2⁄3 7 2⁄3 8 2⁄3
41 7 8 9 260
41.5 265
42 8 9 10 270
42.5 10½ 275
43 9 10 11 280
43.5 9 1⁄3 10 1⁄3 11 1⁄3
44 10½ 11½ 285
44.5 10 11 12 290
45 10½ 11½ 12½ 295
45.5 10 2⁄3 11 2⁄3 12 2⁄3
46 11 12 13 300
46.5 11½ 12½ 13½ 305
47 12 13 14 310
47.5 12½ 13½ 14½ 315
48 13 14 15 320
49 13½ 14½ 15½ 325
50 14 15 16 330

MP stands for Mondopoint. It is a standard (ISO 9407) defined in 1991 to avoid problems of interpretation of shoe sizes. It is mainly used in the field of professional boots (safety) and also for ski boots that address an international market.

The MP corresponds to the length of the foot in millimeters.