A Very Deep Dive on Ski Boots — Part 1: Plastics (Ep.54)

Atomic's global product manager for ski boots, Matt Manser, discusses how ski boots and different ski-boot plastics differ on Blister's GEAR:30 podcast

Intro

Over the next two weeks, we are about to go very deep into the world of ski boots. Here In part 1, we’re going to be talking about the different plastics used to make ski boots. And next week in part 2, we’ll wade into the weird, and very murky waters of flex patterns.

Check out our GEAR:30 episode with Atomic Ski Boots product manager, Matt Manser, and use the (very helpful) detailed notes below as a reference and guide.

Note: For more on Matt’s background, check out episode #61 of the Blister Podcast.



TOPICS & TIMES:

  • What has been the focus of your recent work in ski boots? (2:10)
  • The 3 main families of plastics: PP, PU, and PA (6:57)
  • “PP” — Polypropylene (11:15)
  • How recycled plastics are used in the production process (19:18)
  • “PU” — Polyurethane (23:06)
  • Low-grade PU: Recycled PU (26:53)
  • Mid-grade PU: PU-Ester (27:53)
  • High-grade PU: PU-Ether (31:33)
  • Colors: how they affect plastics’ performance (33:44)
  • What is Desmopan? (38:32)
  • “True Flex” PU — Atomic’s proprietary PU (44:26)
  • How to make a lightweight boot out of heavy materials (49:40)
  • “PA” — Polyamide (53:58)
  • How to verify which plastics your boot is made of (1:00:24)

EXPANDED NOTES: SKI BOOT PLASTICS

Ski boots are made of plastic, and different plastics feel and perform very differently from one another. So knowing (A) which plastics are used in your ski boots, and (B) their pros and cons and general performance characteristics — will help you understand why you like or dislike your current boots, and what you ought to be looking for in your next pair of (typically quite expensive) ski boots.

It’s also a way for savvy consumers to keep manufacturers honest and to verify that the manufacturer’s claims about the types of plastic they used … are, in fact, true.

Each component of a boot can be made of different types of plastics, so be sure to check each of the injected parts (like the lower shell, the cuff, and the grip pad).

To tell what type of plastic a component is, look for a stamp with abbreviations (like PP, PU, PA) and an arrow will indicate which it is.

Furthermore, knowing which plastics were used in a given boot is very useful thing for boot fitters to know before working on a boot, so they will know before they start heating, punching, etc. how a particular boot will respond to the fitting process.

Important Characteristics of Different Plastics:

Durability: Different plastics are more or less resistant to scratches and chips from use. Durability also is a major factor in boot fitting, because certain plastics behave differently when heated, ground, or punched.

Weight: That is, the weight of a particular plastic per volume. Specific weight plays a major role in the overall weight of a boot, along with how thick the walls of a boot are designed to be — which is another factor that’s affected by the plastic type.

Temperature Stability: How similarly or differently the plastic behaves and feels at warm air temperatures (e.g., inside, or on very warm days on the mountain) vs. cold air temperatures.

Color: This includes both the “natural” color of the plastic (e.g., clear, opaque, white, black, etc.), and also how receptive the plastic is to dyes — which affects what designs and styles are possible when using a particular plastic.

Cost: The range of costs of various plastics is massive, and plays a major role in the development, the design, and the price of different boot models.

Overview of Plastics (ordered roughly from less expensive to more expensive):

  • Polypropylene (PP):
    • Generally the least expensive plastic
    • Atomic primarily uses PP in their kids’ boots or price point products
    • General Pros: PP is affordable, lightweight, and temperature stable
    • General Cons: Not durable, not progressive, and not easily fitted, because it can deform under a heat gun or melt during grinding
  • Polyurethane (PU):
    • Represents a step up in performance from PP plastics
    • Most adult alpine ski boots are made from PU plastics — but there is a wide range of PU plastics used for ski boots, from low-end to high-end.
    • General Pros: Produces a “progressive” flex pattern. Good durability. Easily fitted, and can be melted back down and reused.
    • General Cons: Heavy, less temperature stable, and can be very expensive
    • Low-Tier: Recycled PU
      • Atomic chops up and reuses their PUs to upcycle into entry-level adult boots in order to reduce waste during the production process
      • Pros: General performance benefits of PU, more environmentally conscious, and cost-effective
      • Cons: Limited stiffness, and can only come in a black colorway
    • Mid-Tier: PU-Ester
      • Often misleadingly represented by ski boot companies as “PEs” — but shouldn’t be confused with Polyethylene, which fall under the “PP” category
      • Often used for mid- to high-end boots, like junior race boots
      • Pros: Progressive flex, durable, easily fitted
      • Cons: Doesn’t have the “ideal” rebound and damping of more expensive PUs
    • High-Tier: PU-Ether
      • The Gold Standard. PU-Ether is used in World Cup race boots.
      • Pros: Progressive flex, durable, easily fitted, easily colored, can have a range of rebound speeds
      • Cons: Expensive, heavy, not temperature stable
    • Atomic’s proprietary “True Flex” PU
      • Used in Hawx Ultra, Hawx Prime 120, Hawx Prime 130, Hawx Ultra XTD 120, Hawx Ultra XTD 100
      • Pros: Highly temperature stable, allows for lightweight designs, very moldable
      • Cons: Expensive, relatively heavy (but can be shaped into thin walls), not easily colored.
  • Polyamide (PA):
    • Used in touring boots
    • Grilamid: a commonly used, specific brand of “PA”, but not all PAs are Grilamid. (E.g., “Kleenex” is a brand of tissue, but not all tissue is “Kleenex”)
    • Pebax: (while not technically / chemically a PA) can be grouped in this category and can sometimes have issues with punching
    • General Pros: Lightweight, durable, easily fitted, progressive flex (but the flex pattern tends to be ‘springy’), temperature stable
    • General Cons: PA is the most expensive plastic, and it’s difficult to color

30 comments on “A Very Deep Dive on Ski Boots — Part 1: Plastics (Ep.54)”

  1. Have any boot manufacturers tried to utilize carbon nanocomposites(added to the polymer) to decrease weight while increasing stiffness and other physical properties? They are literally one molecule thick and stronger than steel. I believe Head utilizes in the Core series and in tennis rackets. Bayer licenses the technology………….although Head may have an exclusive licensing arrangement…..

    • Hi David, speaking for Atomic, we were one of the first brands (if not the first) to experiment using real carbon fiber in traditional ski boot plastics. In 2011, we mixed real carbon fibers (about the size of a hair from your eyebrow) into our PU plastics in order to make them stiffer and stronger. We call this carbon loading and it acts like putting rebar into concrete. We currently only use carbon loaded plastics in our Backland Carbon ski boots, specifically in the polyamide lower shell.

      As for nanocomposites, this is something that is not currently in our ski boot range but we’re always looking for new technologies and ways to evolve things further. So, who knows what the future will bring.

  2. Really liked the pod cast. I am a nerdy engineer and have designed a lot of plastic parts. I was not familiar with the specific plastics that are used in ski boots. I now consider myself educated. The Atomic speaker was excellent and very clear in his explanations.

    I bet next week your going to talk a lot about FEA analysis and the boot’s spines. I did some modifications on my Lange RS 140’s and was really surprised to understand where a boots stiffness and flex comes from. Looking forward to the next podcast.

    Unfortunately, I don’t represent the general skiing public, but I think this is very good info (although very nerdy-techie) that is useful to everyone. Especially about temperature effects on the different plastics. I hate the 20 minutes by the fireplace of my 140 PU-ether boots. My next pair will be True flex. I recently bought a pair of Hawx Ultra XTD’s and don’t need the fireplace anymore. Yeah.

    Good job.

    PS: Thanks for improving on releasing first looks/flash reviews/full reviews/deep dives at the same time as much as you are able. I for one have noticed and appreciate it.

    • Hi Scott, thanks for the kind words and glad you enjoyed the podcast! Part 2 will definitely be of interest to you as well. And if you are digging your Hawx Ultra XTDs, the normal Hawx Ultra will definitely be the way to go when you’re looking for a new resort-only boot.

      Cheers
      Matt

  3. Interesting statistic would be how many days can you expect out of your shell. I realize this depends on the type of day or just even a ballpark.

    • Hi Bob, the life of a ski boot will greatly depend on a few things: the plastic being used, to some extent it’s thickness (world cup race boots will always last longer since they are built to withstand incredible punishment), and most importantly how well it is cared for. Gear that is abused will always die out faster than gear that is properly taken care of. But, generally speaking, you should be able to get about 150-200 days out of your boots before they lose their feel, fit, and warmth (which is related to the liner more than anything). Boots that are made from PP plastic will die a bit quicker than that for the reasons we mentioned in the podcast.

      Cheers
      Matt

      • Thank you Matt. What a great podcast, really enjoyed it. As an aside Daron Rhahves was my neighbor and I still see him a lot as we are still in the same town. I am sure it is a fine line between weight, wall thickness and durability. I cracked the upper cuff of the Hawx Ultra 110 twice. Not sure if the 130 would have been stronger. Did you make changes to the boot, it was the first year model. Loved how it skied, Daron got a lot of us into it. Great ambassador for you and still one of the best all around skiers out there!

        • Hi Robert, Daron’s awesome and one of my favorite athletes to work with. All around great guy for sure! The first batch of Hawx Ultra boots had some growing pains but we’ve made lots of changes & updates to ensure that kind of stuff doesn’t happen again. Any boot from the last couple of seasons should be problem free.

          Cheers
          Matt

  4. Yes, that is a good question. My rule personal of thumb is 10 days to break-in and then around 100 to 120 full skis days before the boot starts to break down in some way where I start looking for the next boot. I could probaly in some cases extend the life of the boot by replacing the liner but I’ve never loved a boot so much to want to do this. That’s my 2 cents but would be interested to hear what others think.

    At the moment I’m on boots that after 30 ski days and many tweaks still aren’t doing it for me, so sadly they will be getting an early retirement.

  5. I would love to hear the manufacturer input regarding the science behind how long the plastic can maintain is reported flex and progression. I have Tecnica Mach 1 130 boots with zip fit liners, stock liners lasted 20 days, and have over 300 days on them. Buckles started going about 50 days ago, springs in the buckles that hold them open for entry and exit. The shop where I got them said I still have lots of life in them. Also, spring skiing puts lots of salt on the boots, albeit water softener salt, but still salt. I can see an affect on the new buckles. I have a brand new shell ready to go so I will take them out and see what the difference is.

    • Good questions, Bob. I’m talking with Matt a little bit later today, and our “Part 3” episode will be out this Friday…

  6. I do not get rid of a touring boot that fits me until i cannot find parts anymore to repair it.
    It is just too difficult finding boots that fit to buy new boots. Nightmarish really. Changing liners is pretty easy now, the liner companies will help you find the right liner for free. In fact the liner companies are the easiest people to work with when fitting.

  7. can you explain where each ski boot company makes its boots-
    you mentioned atomic and salomon are made in the same factory

    • Hi Joe, Atomic & Salomon share a production site for ski boots in Romania. Even though we share a production site, all product management, R&D, and product marketing between the two brands is fully separate. Salomon does their stuff in France and we (Atomic) do our stuff in Austria & Italy. Once things are green lighted and ready, they are sent to Romania for serial production where shells & cuffs are injected and all parts are assembled.

      For the rest of the industry, it’s going to be a big mix of Italy and Eastern Euroland. The brands will usually have it written/stamped/engraved on the actual boot somewhere.

  8. @onenerdykid

    I’d be really interested in hearing your thoughts on TPU insteps and how they affect flex rating, fit of boots, affect on performance, etc. A lot of companies are putting them in.

    Im in a boot with them and will be replacing that boot ASAP to a boot without it. I feel like it takes the progressivity (is that a word?) out of the cuff. And in feel like a blow through the cuff and use up all my ankle flexion right away.

    • Hi Tim, great insight. One of the main complaints the general skiing population has with ski boots is that they are too difficult to put on/take off and a softer instep zone is used to make the step in and step out of the boot easier. For most Blister readers, I imagine this is not an issue at all, but for the masses this is a huge problem and why so many boot brands add these zones to their boots. We at Atomic think they create too many issues (especially with more aggressive/performance oriented skiers) and is one of the reasons we don’t use them on the vast majority of our boots. None of the Redster World Cup, Redster STI, Redster Club Sport, Hawx Ultra, Hawx Ultra XTD, or Hawx Prime boots have these softer zones. Instead, we rely on selecting the right material hardness and plastic thickness to get the job done. With that said, we do have a boot model (the Hawx Magna) that uses a softer instep zone but we keep its size to a minimum which allows the lower shell to remain very stable.

      Cheers
      Matt

  9. Hi Matt,
    This was a great podcast for a nerdy skier and I’ve got 2 extra questions for you.
    First I’ve seen boots where multiple plastics have been simultaneously injected in a single part. I’m guessing these two separate plastics are generally from the same family and simply different stiffnesses. What is the advantage of this technique, because I’m sure the tooling is significantly more expensive?
    Second are the pu-ethers used in race boots different than what is used in 130 flex rec boots. If so what are the characteristics of these blends that are good for racing but not so for everyday skiing.
    Thanks for doing these interviews with Blister and looking forward to part 2!
    Alex

    • Hi Alex, Yep- when you see two (or even 3) plastics in the shell or cuff, this means the plastics are from the same family (PU & PU or PP & PP etc.) and one is going to be softer/harder than the other. They need to be from the same family to ensure a chemical bond forms where they are joined (there are also mechanical connections present too, like a splice joint in carpentry). The advantages here can be using a softer plastic in certain zones to gain ease of entry/exit, or using a harder plastic to improve power transfer. It just depends on the goal of the zone. Doing this is significantly more expensive since now more molds are involved, more complicated processes are in place, and more labor time to produce everything.

      Speaking for Atomic, the PUs we use in World Cup are the same PUs we use in our 130, 120, and some 110 level commercial boots. And to further that, the Redster World Cup 170 that is commercially available is 1:1 the same Redster World Cup 170 that is used by our athletes. Of course, our athletes will experiment with different plastics and combos, but it is important to us to commercially offer the same stuff that is used in World Cup. We want to be as authentic here as possible.

      Cheers
      Matt

  10. Jonathan once again an amazing podcast, thanks Matt for sharing your knowledge! And Blister crowd for some excellent questions.
    I was wondering does Atomic offer different boots to their racers for different temperatures?

    Where is most of the innovation coming from in ski boots? Is racing/touring tech being trickled down into frontside boots/new materials from suppliers/other sports/new designing tricks such as topology optimization?

    ‘One of the main complaints the general skiing population has with ski boots is that they are too difficult to put on/take off and a softer instep zone is used to make the step in and step out of the boot easier.’
    Luckily Atomic has a solution for that problem coming next season ;) I hope it’ll be a success for you guys. Daring designs fuel evolution.

    • Hi Moos, As with other examples in elite racing (F1, Moto GP, UCI World Cup, etc.) our World Cup athletes do have access to some special things that the general public does not have access to… yet. It is always our goal to bring to market the real stuff that is used in World Cup, it just might take a season or two for it to become available or make its way into the commercial offer. Our commercial World Cup boots that are currently available come directly from what is used on World Cup, 1:1. That means the Redster World Cup 170 that you can buy is the same mold series, last, plastic, liner construction, etc. that is used in World Cup racing. It’s gold standard starting point for all of the World Cup athletes, and as close as you can get to the latest and greatest stuff used by Marcel or Mikaela. These athletes will have a literal arsenal of boots at their disposal, with plastics that have slower rebounds or faster rebounds or other tweaks to suit their specific needs for the event they are skiing, snow conditions, temperature, etc.

      Our ski boot innovation comes from two main areas: World Cup racing and touring. Each of these areas offers unique insights into plastics, flex characteristics, skiing performance, and liner construction that we use in across our entire ski boot range. For example, our ability to make lightweight alpine boots that ski like normal alpine boots came directly from our learnings from the touring boot world.

      Cheers
      Matt

  11. When you order plastic, do you then specify durometer in addition to type of material? Is this typically on the Shore D scale?

    What sort of hardness does a typical 130 flex boot (say the Hawx Ultra 130) use? And the Redster WC shell would actually use a softer material?

    • Hey Greg, We order plastics mainly based on their megapascal unit (MPa).

      I can’t divulge the specific MPa’s we use, but a Hawx Ultra 130 plastic will have a much higher MPa than the plastic that we use in a Redster World Cup 130. This is due Ultra’s thinner construction. In order to arrive at a “130”, we need to use a much harder material to arrive at a similar feel on the foot.

      Cheers
      Matt

  12. How about rebound rates?

    Do you typically spec faster rebound on boots designed for technical events and slower for those designed for speed events? Or is it up to the athlete’s personal preference?

    How about rebound rates for recreational boots?

    • It is more personal preference but it can be event specific & also temperature related. When it comes to racing, there is really not one clear guideline that all of the athletes follow and we will use different mixtures or types of plastic to arrive at the feeling they are looking for depending on their skiing style, event, and temperature at the event.

      We tend to have a fairly “medium” rebound on the plastics we use in our recreational alpine boots.

      Cheers
      Matt

  13. Regarding bootfitting:

    shell punching/stretching: Is there a common reference ‘chart’ of some sort for optimum punching/stretching temps for the various types/blends of plastics referred to in your podcast discussion? Or are the various blends for individual manufacturers so varied that such a chart is not possible? I assume if a customer had the interest, one could contact an individual boot manufacturer and eventually gather the data…but can be time consuming. Personal bootfitting work relied on initially going by ‘feel’ and eventually morphed into using objective measurements by using a laser thermometer and finding the sweet spot for present boots. Hoping to bypass the trial and error phase for the next boots.

    Also: In a recent shell punching/stretching session, I used a system of ziplock bags loaded with snow to apply to heated areas to quickly cool them, check for fit and re heat and push the shell further to reach desired width increases for medial and lateral fore and midfoot areas. This system was very time efficient.

    Are there any liabilities regarding emergent, unforeseen negative effects on the different shell plastics described in the podcast when using this system? For example, could this approach compromise strength/longetivity of certain plastics, but not others…inviting premature wear/reduced ‘flex cycles’, alteration of inherent stiffness and/or potential for cracking in the long term?

    • Hey Swiss, In regards to temperature required to get a boot to “glass transition temperature” (the state of the plastic where it becomes nicely moldable for boot-fitting) it will depend on the plastic being used and the thickness of the plastic. So there are two variables here that will differ wildly between manufacturers. If you only know the actual glass transition temp of the plastic, it doesn’t help since you need to take into consideration the thickness of the plastic in the exact boot in front of you. So a specific chart won’t be of much use to you. The only “good” way to gauge this is to heat slowly and notice when the plastic becomes more shiny- this is when the plastic has reached its glass transition temperature and is ready for punching. For most PU & PA boots, setting a digital heat gun to 240 F / 115 C is a good starting point.

      To your second point, it’s totally fine to heat a boot, stretch it, and cool it down. Adding snow or cooling packs to a heated boot when it is on the press will simply cause the boot to cool down quicker and thus prevent it from shrinking or losing its stretched shape. In fact, we recommend to do this.

      Cheers
      Matt

  14. Great podcast, big thanks to you both! I was wondering last winter why my new Fischer Vacuum boots are crazy springy and you mentioned PA having such characteristics. Had to dig all the way to Fischer’s patent to find confirmation that PA is indeed what they use (for those who are interested: https://patents.justia.com/patent/9949528 ). I just wish Atomic offered Ultra 130 and XTD 130 in size 31!

    • Hi Jussi, If you look around the inside of your Fischer shell (and cuff) I think you will find a stamp that indicates which plastic family is being used. If my memory serves me correctly, it is usually under the boot board in the heel area of the shell, and then on the inside of the cuff somewhere.

      I wish we could make every mold series go up to mondopoint 33, but the demand from the retailer side is simply not there… yet. The more people who mention/complain about this to their retailers, the more they will demand (and order) it from us, and then we (the manufacturers) can get the investments needed to make these sizes. But I definitely hear you, loud and clear.

      Cheers
      Matt

      • Thank you Matt!

        Re the boot sizes, I think there is a real opportunity to differentiate in the race boot market via sizing. No brand offers a race boot bigger than 29 and you could potentially channel some significant amount of demand from other brands to Atomic. Consequently, I would not be surprised if size 30 demand would surpass the demand of size 29 race boots and you could probably sustain this advantage for quite a while.

        Anyway I’ll keep lobbying my retailer of choice as you advised!

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