Dynafit Ski Touring Boot Inserts — Part 3 — Manufacturing

Post by WildSnow.com blogger | September 27, 2017      
The diminutive Dynafit 'tech' insert, what is behind it?

The diminutive Dynafit ‘tech’ insert, what is behind it?

What is an “insert?”
In the case of tech ski touring bindings, what we call “inserts” are a set of two steel parts built into the boot, one in the toe and another at the heel. Even as these are built into the boot, it is crucial to understand that the inserts are part of the binding. The quality of the insert is as crucial to the binding as any other part of the system, and has an enormous effect on binding retention and release.

Part 1
Part 2

Note from WildSnow.com: The original copy and images for this sponsored post were provided by Dynafit, written by Matthieu Fritsch. Lou Dawson did a heavy re-write that involved researching lost wax casting and clarifying the process in English. WildSnow.com maintains 100% editorial control of these posts. We enjoyed working on this and hope we can do more technical manufacturing posts related to specific ski touring gear. Interesting stuff.

While “tech” bindings caught on slowly at first (they appeared tiny and fragile) the slow march to world domination was as inevitable as the rising sun. At a glance, a boot held in a ski binding by pins and inserts appears trivial. A set of holes in the front insert for the toe clamping system, a set of cut-outs in the heel of the boot to accept the heel pins — that’s it. But no.

Dynafit banner. Here is the crux: Unlike an alpine binding system, where you get large boot/binding contact points on the sole, heel, and toe, tech inserts create the only contact surfaces between the boot and the binding. In other words, these are undergoing and transmitting all or most of the forces/stress from the skier’s boot to the binding and also transmitting the ski and binding’s response to the skier, whether you are skinning up or skiing down. The contact surfaces are incredibly small, just a few square millimeters at the toe, not much more at the heel. They’re tiny, but the inserts are subject to surprisingly large forces (up to 200kg on a regular basis, with peak loads around 380 kg, 840 lbs). These forces must be held simultaneously statically, dynamically and over a sometimes lengthy time span due to consumers owning and using boots for multiple seasons.

Thus, not only do the inserts need to be a strong steel alloy, firmly mounted in the boot, but they need excellent fatigue and corrosion resistance as well. Moreover, consideration has to be given to how much the insert wears during the pivoting action of ski touring, as opposed to placing the wear on the binding pins. Ideally, this involves the company making the binding to be the same as that making the fittings.

What are the inserts made out of?
The exact insert manufacturing details are a Dynafit secret recipe — the result of over 30 years working on the system. What can be said is both toe and heel inserts are made out of a complex steel alloy, and are then heat treated to reach the desired level of mechanical resistance and hardness before receiving a zinc based coating for better friction behaviour and also corrosion resistance. Top secret details aside, plenty can be shared about the overall process of lost wax casting used to make the fittings. Below, the casting process in detail.

(Note from Lou: It appears only one of these photos shows actual binding parts, others are representative of the process and are “stock” photos from the manufacturing company. They’re good images that do a decent job showing the various steps of lost wax casting, so we’re happy to use them — though I wish I’d been there in the factory with my camera, dodging molten steel and living to blog about it.)

As with much manufacturing these days, the insert building process begins with a computer aided design. Once the insert’s digital 3D model is validated, a physical mold is made, which in turn is used to produce wax models of the inserts (in a process similar to plastic injection molding). In other words, you end up with wax versions of the inserts. These wax models are almost one-to-one in size, the same as the final part. This is where casting technique know-how comes in, as any hot handled material will shrink while cooling down, so getting the wax model’s dimensions right is part art and part science.

As the wax models are made they are all attached together to form a “tree.” Quite a few are glued to one wax "trunk."

As the wax models are made they are attached to a “trunk” forming a “tree.” This allows many small parts to be cast in the same steps. Each model’s attachment to the tree will eventually form a channel for molten steel that’s poured into a funnel at the top of the tree. Pictured here, Dynafit binding “triggers.”

The "tree" is then coated in a liquid ceramic-type material to allow a special ceramic sand to stick to it. This is the step where the “real” casting mold is created. The process  consists of repeating the same procedure of liquid/sand/liquid/sand. A rougher sand is used at each step.  The finest sand is used at first because this is the one which will define the final surface roughness of the cast product.

The “tree” is then coated in a liquid ceramic-type material that allows a special ceramic sand to stick to it. This is the step where the “real” casting mold is created. The process consists of repeating the same procedure of liquid/sand/liquid/sand. A rougher sand is used at each step. The finest sand is used first because this material defines the final surface roughness of the cast product.

The sand coating part of the process, this is repeated several times, alternating with the liquid coating pictured above.

The sand coating part of the process, this is repeated several times, alternating with the liquid coating pictured above. Product molds shown here are apparently not Dynafit insert parts.

Once the ceramic sand coating is completed, a several hour drying period ensures that the mold reaches a sufficient mechanical resistance to handle the next steps. Continue reading, it gets dangerous now.

Once dry, the parts are brought into an autoclave which is going to dry out the ceramic completely and melt completely the wax to remove it from the ceramic. This the birth of the casting mold. A hollow ceramic shell, or mold: the cast.

Once dry, the parts tree is placed into an autoclave oven. This completes drying the ceramic sand coating and melts the wax out. This is the birth of the casting mold: a hollow ceramic shell is the cast.

Now we are at the spectacular and the most dangerous phase of the manufacturing: the casting.

Now we are at the spectacular and most dangerous phase of the manufacturing: the casting. In the case of making Dynafit inserts or for that matter any other quality product, a special metal formulation is required. To create that, the specified amount of each base material is placed in the furnace to create liquid steel. The special sauce is then heated up to a specific temperature, ending up liquefied and pourable. This part of the process can involve other tweaks, for example sometimes a high temperature “resting” period is required to make sure the metallic mixture “base material” will form specific compounds. Overall, highly technical metallurgy, nothing less.

While the base metal is concocted and liquified, the ceramic molds are placed in another furnace

While the base metal is concocted and liquefied, the ceramic molds are placed in another furnace and heated to a similar temperature (900 to 1000°c) as the liquefied base metal. This is done to avoid thermal shock, as the liquid metal will be poured into the ceramic causing it to shatter if the temperatures are not equalized. This is another phase where an experienced manufacturing team is crucial. More, depending on the type of material behaviour desired, the temperature of the mold has a significant effect on how the liquid metal will start to cool down and harden. This will influence the cooling speed, thus the material structure. As you can imagine, in the case of ski boot tech inserts, this part of the process can make or break the necessary metallic performance in terms of wear and friction.

Afterwards, the molds are taken out of the furnace in order to fill them with liquid metal. This phase is extremely dangerous. At this point the liquid metal is at a temperature above 1100°C, 2000°F.

After the wax is lost and the molds are properly heated, they’re removed from the furnace in order to fill them with liquid metal. This “pouring” phase is done by hand and extremely dangerous. The liquid metal is at a temperature above 1100°C 2000°F. Don’t wear your trail running shoes.

After the pour, a cooling period is observed either in open atmosphere or under controlled conditions, depending on what is expected of the steel alloy.

Once everything is cooled, the molds are vibrated in order to break the ceramic shells off the actual steel parts.

Once everything is cooled, the molds are vibrated in order to break the ceramic shells off the actual steel parts.

The next logical step is to cut each part off the "tree trunk" Cutting the parts off the trunk

Next, each part is cut from the “tree trunk.”

When required some surfaces can be either polished or milled in order to achieve a better surface finish

When required some surfaces can be either polished or milled in order to achieve a better surface finish (clearly not a boot insert shown here!)

After the finish work, quality control is done to ensure that the inserts are fulfilling the dimensional and chemical specifications. Furthermore, x-ray analysis is performed (on a statistical basis, not on every piece) to ensure that no microcracking occurred within the part structure during the cooling process. After this the inserts are sent out for heat treatment — an essential step that immensely increases their strength and resistance to friction wear. Final step, the inserts are zinc coated to provide good friction performance and protect from corrosion.

After zinc coating, a final automated 100% dimensional check is performed, and the inserts are sent out to the boot manufacturers. Most boot makers will also do their own quality control checks on the fittings, though generally not as extensive as the original manufacturer.

The challenges don’t end. Mounting the toe insert in the boot’s injection mold is difficult. The various boot makers are secretive about how they do this, the challenge is that in any plastic injection molding process, there are minimum size restraints on the areas you’re attempting to inject. Start adding things inside the injection mold, you can end up with trouble getting the plastic to fill the mold. Moreover, as noted above you’re trying to mold a small steel part into a small volume of plastic — and expect it to withstand large forces. Takeaway: Be appreciative of what you have on your feet when your tech fittings, bindings, and body are pumping along as one integrated unit, climbing mountains, and carving turns on the down.

Part 1
Part 2

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Mixing steel for making Dynafit boot tech inserts.

Mixing steel for making Dynafit boot tech inserts.


Please Enjoy A Few Suggested WildSnow Posts


17 Responses to “Dynafit Ski Touring Boot Inserts — Part 3 — Manufacturing”

  1. gino September 28th, 2017 8:19 am

    Wildsnow is becoming more and more a subsidiary of Dynafit brand…… congrats Lou continue on this way. Sad.

  2. Lou Dawson 2 September 28th, 2017 8:48 am

    Gino, I beg to differ, we’ve been supported by Dynafit banner advertising for years, does that make us a “subsidiary” any more than any other publication with advertising?… due to complaints (and our own opinion) about banner advertising and how it clutters up the website, we’ve been trying to shift from banner advertising to direct support of sponsored posts, which are virtually the same thing we’ve been doing for years — getting paid to write by our advertisers. (The shift away from banners is slow, but it’s happening, though for the foreseeable future I’d imagine will have a few banners kicking around, just not so many.) Key is we agree to 100% editorial control and the proof is in the pudding. If you think our posts are a “subsidiary” and not of value, you’re welcome to not read them. But we slave over these posts with only one purpose, to provide authentic value to you guys. Instead of guessing we are a “subsidiary” (whatever that exactly means) how about some direct feedback on our writing, so we can improve it?

    More, is there something inherently wrong or immoral with being a successful writer running a blog supported by direct advertising sales? Any more so than a magazine, or newspaper?

    Again, if our content doesn’t produce value for you, so be it. It’ll go away because it will not get read and readers will not produce advertising views. Problem solved for you. The “subsidiary” will cease to exist.

    As to this post in particular, we worked our behinds off on it, as I thought the manufacturing process would be interesting and perhaps helpful for everyone. Dynafit was key in that, as they rounded up the factory photos and provided raw material German/English text that I used as a source for the writing.


  3. Eastskier September 28th, 2017 9:12 am

    It’s inevitible, Lou publishes a few Dynafit oriented blog posts, someone comes along, ignores the massive amount of content here that covers other companies, and says he is “biased” or a “subsidiary”. Laughing out loud. Lou, thanks for your hard work.

  4. Lou Dawson 2 September 28th, 2017 9:19 am

    World domination by Dynafit is only a week away, so I hear! I doubled their advertising rates so we can stock up on prepper food packs and ammo.

    Please check here for survival kits, so we can make obscene profit off affiliate sales as a subsidiary of Backcountry.com



  5. Jim Baugh September 28th, 2017 9:21 am

    Thanks for posting this detailed description in what makes a Dynafit insert. Having dabbled in lost wax casting while in college I found this article fascinating.

    It is cool to see a glimpse of all the work that goes into this game changing technology.


  6. Lou Dawson 2 September 28th, 2017 9:31 am

    Thanks Jim. Thing to remember here is that Dynafit (and Fritz before that) were working on the best process for fitting manufacturing _long_ before anyone else did. Detailing their process, which they refined, only makes sense. Other companies who make fittings probably use a similar process — and they’re standing on the shoulders of Dynafit and Fritz, reality. I’m delighted Dynafit decided to work on these “fitting” posts with me. This is the last of them, BTW, though we’ll continue curating and working the comments. Thanks, Lou

  7. See September 28th, 2017 9:45 am

    I hope you’re not using most enthusiast publications as your standard of journalistic objectivity, Lou. In my opinion, Wildsnow has higher standards than most magazines. The factory tour type posts are some of my favorite Wildsnow content, and of course the manufacturer gets mentioned in these pieces. Thanks.

  8. Lou Dawson 2 September 28th, 2017 10:10 am

    See, good point. No, I’m not basing my standards on the “standard” publication, but rather on my own study of the issue as well as personal ethics — along with paying attention to you guys making well supported complaints or showing how you like things by the amount of traffic you generate. Main thing I do is think very carefully about how to make our posts authentic and as unbiased as humanly possible. I do feel that most if not all writers, including myself, have inherent bias that’s part and parcel to pumping out words. I watch for that but some bias in my opinion is just the way it is. For example, I’m biased as to ski touring being the best sport on the planet, if not in the universe. Or joking aside, I’m biased as to gear weight being an important factor in evaluating products. And so on.

    One of our main biases here is we generally only review gear that we like. That policy could result in someone thinking we are “biased” towards a particular advertiser, if said advertiser happened to make a lot of good gear. That’s how we roll, aint gonna change that one. If someone else wants to base a blog on doing negative reviews they’re welcome to that minefield — more power to them.

    As to bias towards a particular company, due to their financial support, I’m always watching myself for that sneaking in.

    Another thing to remember about Dynafit in particular, is when WildSnow began publication they were pretty much the only company making gear we liked for the sport, especially bindings. If you count all our posts, 3,813, even considering that, only about 7% of those posts are Dynafit oriented — and some of those are critical, for example covering various forms of breakage. Over the past 50 posts or so, there have been 5 or so specific Dynafit posts, that with Dynafit still being the biggest player in the field, in terms of having a vertical product line. Biased subsidiary? In fact, I think someone at Dynafit was wondering what was going on and wondering if I was a subsidiary of someone else!

  9. Lou Dawson 2 September 28th, 2017 10:17 am

    BTW, the definition of “sponsored post” is whacked all over the place in the industry. On some websites, it means you’re reading an advertorial. I hate those as much as anyone. Our “sponsored posts” are simply an honest statement that we have an advertiser and they’re financially supporting our writing, with some posts specific to them that are usually the result of an agreement between them and us as to subject matter. Again, with 100% editorial control on our part, as well as right to refuse anything. The overarching goal is to get away from banner advertising, both so you guys don’t have to endure a cluttered website, fooling around with ad blockers, etc., but also so we can focus more on content instead of managing an ad server, which I despise nearly as much as how difficult our content management system has become. Lou

  10. Rudi September 28th, 2017 11:21 am

    This was a great article and I really enjoyed learning about the process. I am continually astounded by how well the toe fittings hold up considering they are smashed and ground against rocks all season. If only the boot plastic looked as good!

  11. JCoates September 28th, 2017 2:33 pm

    Lou, try to keep a thick skin. Most of us realize you’ve got a difficult job–trying to write honest reviews while still making a living suckling off the ski industry teet.

    Your honest reviews do have an impact, however, and I think some of readers get nervous when we see “sponsored by” on a post. Consider how much changed from the TLT5 to the TLT6. Most (if not all) of the things you said you didn’t like about the 5 got changed for the next iteration. So–for us readers of the most popular ski touring blog on the net–please don’t forget that your continued objectivity makes a huge impact on improving the best sport in the universe (even if I still liked the metatarsal flex on the 5 and wish they kept it).

    Thanks, though, for all the work you put into the site and improving the sport.

  12. benwls September 28th, 2017 2:51 pm

    Interesting post. Thanks Lou.

    I’d like to see the process for making the original Salomon Quest fittings. It was probably a little less rigorous than what we see here.

  13. Lou Dawson 2 September 28th, 2017 4:34 pm

    JCoats, thanks, I really should give you guys the last word on anything, but I can’t help my get a bit defensive about the tired old “Dynafit bias” concept.

    As for the “Sponsored by,” the whole mess with online advertising is such a smoke and mirrors scene. Here at WildSnow, all our posts are “sponsored,” by our advertising “sponsors.” Going one step farther and letting them stick their brand on a particular post, in our case is no different, though I totally understand how it might look, especially to folks who don’t carefully read our content and are used to “sponsored” content being the mostly lame stuff it is throughout the internet.

    I actually tried hard to come up with some other terminology, like “partner” as “sponsored” is such a loaded word. But I’ve not done well with that. Suggestions welcome.

    Bottom line is when ad blockers began to be used by people who want free content from people who work for free and live on tree bark and grass cuttings, that forced publishers to get creative. Tying the content closer to the advertiser is one such approach. It’s like, if you want to block advertising, block my content as well. Fair enough?

    But you already know all that stuff. I’d say to anyone, if our content doesn’t hold up, “sponsored” or not, I’m well aware that our readership will die off and that will be that. Thus, the whole thing is self regulating.

    And yes, I be suckling, as much as in humanly possible (smile)!

  14. bill September 28th, 2017 7:05 pm

    Hey Lou
    Thanks for a great post.
    For me it is great stuff to see.
    Too bad you had to take a snark for it.
    I think your standards are unsurpassed.

  15. Bard September 28th, 2017 9:57 pm

    Thanks Lou. The intricacies of casting still blow me away. A friend of mine makes hollow bronze castings in a homemade forge! Weren’t you a BD Homer a while back, lol. Don’t sweat the haters:)

  16. Pierre Gaudreault October 3rd, 2017 10:16 am


    Thank you for your post about any bindings, i appreciate them all. With your humor, your knowledge and your vast experience. I really appreciate the works you’re doing to explain and validate all the manufacturers claim.
    Than you again to you and your TEAM.

  17. Lou Dawson 2 October 3rd, 2017 12:06 pm

    Thanks Pierre, it is indeed the team. Hopefully lots more this coming season… Lou

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  • Welcome to Louis (Lou) Dawson's backcountry skiing information & opinion website. Lou's passion for the past 50 years has been alpinism, climbing, mountaineering and skiing -- along with all manner of outdoor recreation. He has authored numerous books and articles about ski touring and is well known as the first person to ski down all 54 of Colorado's 14,000-foot peaks, otherwise known as the Fourteeners! Books and free ski touring news and information here.

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