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Ski Construction Explained: How Do Materials & Manufacturing Affect Performance?

Have you ever wondered what’s hiding beneath the visible parts of your ski? What gives your ski its pop or edge hold? Or what the fuss over carbon fiber stringers is all about? This guide to ski construction takes you from the center of your ski to its edges, explaining how skis are built and how materials and manufacturing techniques can affect your skiing.

Table of Contents

Ski Cores

Composite Layers

Plastics

Metals

Ski Cores

Manufacturers have explored a bunch of different materials for ski building over the past 40 years. While some materials have enjoyed a fair bit of success, the bulk of the market remains relatively unchanged. The core is the single most important part of a ski because it defines a ski’s character and flex. The most popular skis of the past 40 years have all used wood cores, and that continues to be the gold standard for ski construction.

Wood

Wood-Core-1

Pictured is a ski featuring a full wood core after the sidewall was removed.

There are very few other pieces of modern sporting equipment that still rely on a natural material like wood. Everything else is plastic, metal, or textile based. Can you imagine if snowshoes or tennis racquets still had wooden frames? So why continue to use wood despite its high cost? Because it’s the perfect material for the job. It has a combination of properties that you simply can’t find in anything else.

The most important property imparted by the wood core is its ability to store energy. As the ski is weighted (picture a tightly coiled spring) the core loads up. As the skier exits the turn, that energy is released, a feeling often described as “pop.” Because of this, a wood-core ski feels more responsive than its foam-core brethren.

Wood has a very different stiffness than the fiberglass and plastic that surrounds it in the ski, and as a result, vibrations are damped out and wood-core skis feel very stable. Wood also has more stable properties than foam and, because of this, it’s less likely to degrade and lose camber and stiffness over time.

The type of wood used varies ski to ski, and many skis use several different types of wood laminated together to achieve a specific set of handling characteristics.

Shitfoam

foam_core

Pictured is a ski featuring a full foam core, manufactured using cap-style construction.

There’s a small problem with wood cores, however. They’re expensive. Thus, for low-end skis or the rental market where performance isn’t a top priority, the industry went looking for an alternative to wood cores. The answer was something that I affectionately call Shitfoam. Many manufacturers injection mold a PU foam into the shape of the core. Shitfoam cores are cheap, but they have a number of downsides. They’re generally less strong than a wood core, they lose camber and stiffness more quickly over time, and they don’t have the same “pop” and rebound energy that we associate with a lively ski.

High-Performance Foam

Not all foams are created equal. Unlike Shitfoam, some foams are carefully engineered to have high strength and exceptionally low weight. While these high-end foams can often be quite expensive, they have a very unique combination of properties. On their own, however, they’re often described as feeling “tinny” or prone to vibration and chatter. When used in conjunction with wood (with strips of each material in the core), one can achieve the best of both worlds: skis that are lightweight, but still maintain the damping and “pop” that make wood core skis so desirable.

Composite Layers

The next stop on our tour through the center of a ski is the composite layer. “What the hell is a composite?” you might be wondering. Glad you asked. Composite material gives a ski most of its stiffness and also sticks the core to all of the plastic components. The composites used in skis have two components: some type of fabric and some type of epoxy. Each component would be useless on its own, but together they create a strong structure. Before a ski is made, the fabric is floppy and pliable, like a T-shirt. The epoxy is a thick, sticky liquid, like honey. When they’re combined during the manufacturing process with heat and pressure, the epoxy solidifies and bonds all of the layers together. It also aligns all of the fabric’s fibers, gives them stiffness, and allows them to transfer loads to the other layers. Magical!

For the most part, everyone in the ski industry uses a similar type of epoxy. Thus, the main difference between composites is the type of fabric the designer decides to use. Each type of fabric has different properties and comes at a different cost. Fabric fibers can also be woven in different ways to increase torsional stiffness or bending stiffness.

compositesThis composite ski utilizes wood, plastic, fiberglass, and aramid in its construction.

Fiberglass

Perhaps 90% of all skis on the market use only fiberglass as their fabric. And there’s a good reason for this: it’s an awesome material. It contributes a lot of stiffness (for most skis, in the neighborhood of 50-80% of the overall stiffness), and it can bend a really long way before breaking. When combined with a wood core, it has a really nice responsive-but-damp feel to it.  The type of fiberglass used in skis today is essentially unchanged from when it was first introduced in the early ’60s. Chances are your favorite pair of skis is made of plain old run-of-the-mill fiberglass. As a raw material, fiberglass looks like any ordinary white fabric. It could easily be confused with a tablecloth. However, when epoxy is applied to it, the fibers become translucent. Manufacturers are growing fond of leaving topsheets clear to allow consumers to look in at the core. The fiberglass layer is the cloudy pattern you can see above the wood grain.

One of the biggest reasons for the popularity of fiberglass is its low cost. It does, however, have a major handicap when compared with other types of fabrics: it’s heavy.

Carbon

The second fabric that people are commonly familiar with is carbon fiber. In the past ten years, it’s become ubiquitous across a number of industries, from bikes to car parts to kayaks. Carbon comes at a much higher cost than fiberglass, but it’s much lighter for a given amount of stiffness. This allows designers to make carbon skis with very similar stiffness and flex to fiberglass skis, but at a fraction of the weight. This becomes especially important in touring skis and splitboards, where weight is of the utmost concern.

Whenever a ski flexes, the top side of the ski is put into compression and the bottom side of the ski is put in tension. This stresses and strains the fibers and, because of its high stiffness, carbon fiber is prone to buckling. Due to this problem (and also carbon fiber’s high cost), manufacturers will often just add carbon fiber “stringers” to a ski. These are basically thin strips of carbon that help reduce overall weight, without sacrificing too much money or strength. It’s important to note, however, that while marketing departments are quick to wave their carbon banners around and sing from the rooftops about drastically reduced weight and the additional “pop” that carbon provides, carbon is sometimes used in such small quantities that the average skier would never notice the difference. That said, it’s easy to rationalize any decrease in weight when you’re hauling your skis up a couple thousand feet of mountainside.

Aramid

There’s only one other type of fiber that’s used regularly within the ski and snowboard industry, and that is aramid (commonly known by the trade names Kevlar and Nomex). These materials are widely used in bulletproof vests and fire-protection equipment, but they have other properties that make them excellent for ski building. Aramid is also lighter for a given amount of stiffness than fiberglass, but it’s most often chosen for its ability to damp vibration and absorb impacts. Due to its high cost, it’s rarely used in large quantities, but it can have tremendous effects on ski designs that are otherwise too chattery or vibration prone.

Plastics

Plastic. For as little as it contributes to the character of a ski, plastic is basically all you see when you look at a ski on the rack. Various forms of high-performance plastic are used for the base material, topsheet, and sidewalls. The main function of all of these different types of plastic is to protect the ski from the elements and allow it to slide on snow.

plastics

 Plastics make up the base, sidewall, and topsheet for most skis on the market today.

Base Material

All manufacturers use ultra-high-molecular-weight polyethylene (UHMW-PE) for ski bases. It comes in many colors and can be cut to form intricate designs. It can be purchased in many different thicknesses, but most base material is only a millimeter or 1.5 millimeters thick (and sometimes even thinner by the time it gets stone ground at a shop a few times). The most important performance attribute of UHMW is that it slides well on snow. That said, base material also takes a lot of abuse from impacting sharp objects like rocks and abrading on sharp snow crystals over time. Thus, it needs to be tough and durable. Base material can be formulated to be harder or softer depending on the needs of the customer, but hard base material can be much more difficult to finish.

There are generally two types of UHMW on the market that are used in skis: sintered and extruded. Extruded UHMW is made by heating up the plastic and forcing it through a die—much like a soft-serve ice-cream machine. This process is cheap, but it doesn’t allow the base material to hold wax very well, so it’s only used on low-end skis or specific models where glide isn’t as important as the price point. Sintered UHMW is made of a very fine powder that’s compressed and heated (just below the melting point) for a very long time until it solidifies into a big doughnut shape. Then the thin material is shaved off from the outside in the desired thickness. Sintered base material is preferred over extruded because its tiny pores can accept wax, which results in a ski with superior glide.

Topsheet

The topsheet protects the rest of the ski from water intrusion and also serves as a platform to decorate the ski. Topsheet material can be made of several different types of plastic, and each has its own specific benefit. Topsheets’ main functions are bonding well to the rest of the layers, resisting chipping from ski edges, and having good clarity for displaying graphics.

Three different technologies are commonly employed to print on topsheets: screen printing, sublimation, and direct digital printing.

Screen printing is the most common and is the same method used to print basic T-shirts. A layer of ink gets spread across a big stencil and pushed through onto the topsheet. Each color of ink is applied one layer at a time until the graphic is completed. It’s a cheap and simple process that’s been used for ages.

Sublimation is a lot like applying a temporary tattoo. The graphic is printed onto paper, and then heat and pressure transfers ink from the paper onto a topsheet. Sublimation allows a wide variety of colors (and gradients) to be printed at one time, but it’s also typically more expensive and technology intensive than screen printing.

The last common printing method is direct digital printing. In this method, the topsheet material is loaded into the printer like a roll of paper, and the ink gets applied directly to the topsheet. This requires expensive equipment, but achieves crisp, clear graphics and produces no waste paper like sublimation does.

Sidewalls

Plastic is also used around the outside of “sidewall”-style skis. Generally, this plastic layer gets attached to the core before the ski is pressed and gets bonded to the rest of the ski with epoxy. Most folks claim that a sidewall ski holds a better edge than a “cap”-style ski, in which the topsheet comes all the way down to the ski edges, because there’s more material digging into the snow on each turn. In addition, because the plastic sidewall is much less stiff than the surrounding ski materials, it can help to damp out vibration.

The three most common materials used for sidewalls are TPU, ABS, and UHMW. TPU is the cheapest and offers good impact resistance, but it’s denser than the others and creates a heavier ski as a result. ABS offers a good blend of mechanical properties and impact resistance, but it’s not cheap. UHMW also offers good mechanical properties, slides on snow more smoothly than the others, and is fairly lightweight. That said, it’s costly and can be difficult to bond to the other layers of the ski. Each of these types of plastic comes in a wide range of colors and can be decorated with screen printing if desired. Because of the cost of these materials (and the amount of waste associated with the manufacturing process), many manufacturers are moving to hybrid sidewall-cap designs that incorporate sidewall material in high-wear areas, but remove it from tips and tails where it adds weight and unnecessary cost.

Metals

The last piece of the ski puzzle is metal. For most skis, metal only shows up in the edges, but some skis make use of metal to reduce vibration, transmit power to the edges, and provide a more secure mounting platform.

Edges

edge-bundleEdges dig into the snow to allow you to turn. Back in the early days, when skis were only made of wood, skiers had very little control, and retro videos make that very clear. Screw-in edges were a vast improvement and all of a sudden, skiers everywhere were working with sharpened knives. They were basically short sections of steel that you could screw in all along the edge of the ski, and change out if they broke.

Edges have come a long way since then, and they’re now built into the structure of the ski during the manufacturing process. The part that you can see from the outside is only a small portion of the edge; there are also little “teeth” that extend over the top of the base material and are bonded to the rest of the ski with epoxy.

The most important property of an edge is hardness (it must maintain its sharpness after a couple runs), and because of this, almost all edges are made of steel. However, they also need to be ductile enough that they don’t crack or blow out when you slide a rail or accidentally hit a rock. There are only two companies in the world that make steel edges, and they each have proprietary steel formulas to achieve the desired properties. Manufacturers will choose different types of edges depending on the ski’s use. A touring ski will have thin, lightweight edges, and a park ski might have extra thick, ductile edges.

While most edges are conventional steel, stainless steel edges are also available, and they’re used primarily to mitigate edge rust during shipment or use. However, stainless tends to be softer (i.e.: edges get dull faster) and it’s substantially more expensive.

edge-install

Edges being carefully installed at the 4FRNT factory.

Titanal

It’s also possible to use a certain form of metal in the actual ski laminate next to the core or fiberglass. Because of the amount the metal has to bend, however, this requires a specific type of metal that has high stiffness but can also bend and flex with the ski without cracking or yielding (becoming permanently bent). This material is called “Titanal,” and only one company in the world makes it, due to its unique combination of properties.

Titanal adds stiffness to skis and is often found in stiff all-mountain skis and racing skis. Even in these high-performance skis, manufacturers typically only use a sheet that’s about a half-millimeter thick. The other great benefit of Titanal is that it damps out vibrations because its bending stiffness is so different from the other materials surrounding it.

Though it sounds like “Titanium,” Titanal is actually an aluminum alloy that includes no Titanium. However, there are other metal laminates that do contain trace amounts of Titanium. When you read a product description that says a ski has a Titanium laminate, that actually means it has an aluminum alloy laminate with only a very small amount of Titanium in it.

Mounting Inserts

The last use of metal in skis is for binding inserts. While these are ubiquitous in the world of snowboards, to allow for adjustment of bindings, they’re seldom used in skis. They came about as a solution to the issue of binding screws pulling out during use, the idea being that a binding screw can thread into them perfectly and the insert will distribute the forces of skiing across a much wider area, reducing the chance of the screw pulling through. They also make for quick, easy adjustments of binding-mount locations without having to drill new holes or deteriorate the structure of the ski.

There you have it: a guide to the components of a ski’s construction, and, hopefully, a better understanding of how that construction affects the ski’s performance.

Ski cores and manufacturing images courtesy of 4FRNT Skis.

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6Comments

Here's what the community has to say.

l.k105807364

l.k105807364

Hi and thank you for the great piece! I am currently in the process of designing my own ski rack, and was hence wondering if there are any specific materials that could harm the skies that i would use in the construction of my ski rack. I was therefore wondering to of what material I should best construct my ski rack, in order to not damage the skies, and have a long lasting sir rack?
Thank you for all your help!

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Craig L.

Craig L.

Peter, You are correct on your presumptions on cap versus sidewall skis. Tooling is a lot more precise and costly on a cap ski, but the finishing is a lot cheaper. They are typically used high volume low cost skis to save manufacturing costs.. Also once the ski is designed, you can't change anything. All your components have to fit precisely. Race skis are made with sandwich construction because they are typically lower volume, plus on the higher level the builders might add more metal or other materials depending on who the ski is built for.



Bottom line, there have been a lot of crappy skis built with cap construction and they have a bad rap because of this.

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hag105356620-0

hag105356620-0

Hi, i'm planning to build a full composite snowboard (except edges) whit combination of every three type of fabrics, carbon, fiberglass and kevlar. above information was very very useful, whats your opinion about my planned board. i will use a honycomb fiber in the middle, and the base will be Kevlar. would you please tell me if i am not in the right way!! thanks

i live in Iran and here there is not that much possibilities and varieties of different materials.

Regards

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Keith Flanagan

Keith Flanagan

Quality of material is definitely very important specially in terms of construction. If your house is made with poor quality material then there may be a risk of damage to building very early.

http://amfsteel.com/

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Jamsie

Jamsie

Awesome piece! Great info, I understood a lot of this in general terms, but it is nice to put specific labels on some of these materials. Thanks! I was thinking about what Peter brings up in the above comment about bike frames vs skis and damping quality. I'm not nearly as brainy as he seems to be, but I worked in bike manufacturing in the early nineties when much of this was being developed. The big difference here is that, as Dwyer mentions above, the ski is essentially a "spring" where in a bicycle frame the objective is to minimalize any spring force provided by that frame ( suspension components excluded of course). Application of materials to provide both spring force and damping quality depends upon many variables, including but not limited to: shape or form, amount, quality, and how those materials attach or interact with the other materials in the system. My experience is that the best product designs emerge out of a combination of good science and good old fashioned field testing. In outdoor sports much of this testing gets done by the end user, making development a slow process. The good news is most of us don't mind. I just love to be outside, and trying out some new gear somehow always adds to the experience, even if it's just to give me something to gripe about with my buddies. All that being said... Road frame? 4130 butted Cro-Mo. Some things just don't need fixin' my friend.

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Peter Wadsworth

Peter Wadsworth

Dr.Dwyer,

Thanks for the write up! Love that you killed the titanal=titanium fallacy...personal pet peeve of mine.

I've got a few questions.



- Can you call BS or truth on a theory I've got?

You state "Most folks claim that a sidewall ski holds a better edge than a ?cap?-style ski." I've heard this a lot too, and my personal experience backs this up. But, my "I went to engineering school" theory is that the edge hold has little to do with Cap vs. Sidewall. In my head, a Cap ski should be more torsionally stiff because the cross-section moment of inertia will be higher than a similar sidewall ski (http://en.wikipedia.org/wiki/Bending_stiffness). This added torsional stiffness should make the ski edge better. buuuuuuut....since cap skis don't have the damping from the sidewalls they're usually not made as stiff. And/or, cap skis are designed primarily for lightweight or low-cost. These factors mean that cap skis are generally targeted at skiers that don't value aggressive edging as much. It's a chicken/egg thing ( *I* think). It's not that cap skis don't edge as well, it's that skis that aren't made for aggressive edging are usually made with cap construction for other reasons like cost and weight. Think there's truth in this? Or am I full of it?



- Ever notice that bicycle manufactures claim carbon frames give a smooth ride by damping vibrations and road buzz, and that aluminum frames are super stiff but "buzzy"? Then ski manufacturers say that adding an aluminum sheet to the ski makes it damper and putting in carbon makes it stiff but chattery? I know that marketing is 99% BS, but how can two similar industries claim the complete opposite from these two materials? What's your experience actually making stuff with these materials?



- What's your experience using wet layup vs pre-preg composites? Can you tell us at all about the trade-offs in ski design? Is a lot of weight actually saved using pre-preg?







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