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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Edges 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.
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.
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.