Cores, edges, sidewall, topsheet. That’s just the beginning of a ski’s construction elements. What are they, and why are they important to you when you get on the snow? We’re breaking it down so you can impress your friends on the lift.
Previously, our ski design guru Olaf took you through the definitions of Camber, Rocker, Sidecut and Taper, so now you should have a basic understanding of how the shape of your ski interacts with the snow. This time, we’re discussing the anatomy (or guts) of your ski, and the role that each piece plays.
The best way to do this is to chop a ski in half, and start from the bottom, up. Don’t literally do that on your own, that’s just a waste of a good ski.
People constantly say “Well aren’t bases just P-Tex?” They’re wrong, but think of P-Tex as a brand name, kind of like ChapStick – except in this case it isn’t some glorious lip moisturizer, it’s actually a brand name of Ultra-High Molecular Weight Polyethylene (UHMW-PE). This is a very durable plastic product that has micro-pores that open to accept wax, and contract to hold it there. It’s great because it performs well at a variety of temperatures, and is very easy to bond to when producing the skis. The biggest conversation we hear everyone talk about is extruded vs. sintered, and a common misconception is that they are a different material. Nope! This designation refers to how the UHMW-PE is made in to sheets. The first method, extruded, is much like pasta where a large amount of viscous material is pushed through an opening to make a sheet. Sintered material combines the PE on a molecular level at a temperature and pressure just short of melting, so that the material never actually becomes viscous. For both methods of production there are different molecular weight finished products, the general rule of thumb is the higher weight the less porous and faster the base.
I will start off with a broad statement that may come as a shock to most of you, but all edges are created equal. Believe it or not, but there are only two widely used ski and snowboard edge producers in the world. What we do have control of, however, are how our edge teeth are configured and the Rockwell hardness of the steel (and in some cases further heat treatment of the edges). Edge teeth refers to the portion of the ski edge which you can’t see, because it’s embedded in to the ski. This is what holds your edge tight between your base and your core (along with rubber which we’ll discuss later). In almost all cases that I’ve found, the thickness of this section is 0.7mm thick, but what we do have control over is the configuration of the teeth. Here, at Armada, we use a solid rail with perforations, rather than what you might typically see as a “T” type tooth. We do this so that in the event your edge cracks, there is a greater chance of the edge staying in tact rather than being ripped out. Then the basic dimensions you have are the height, width, and step. The height refers to the overall height of the edge, the step refers to the height of the edge where the base will occupy, and the width refers to the measurement of the edge that contacts the snow.
The hardness of the steel is also a measurable characteristic, and most edges you see are going to be Rockwell Hardness 48 on the C scale. This hardness is determined by a standardized test in which a machine indents the steel, and they are broken down in to 7 categories (A-G). Some companies use softer metal on their park skis to promote deformation rather than cracking.
The rubber in your skis serves two purposes: the first is to create a bonding (or shear) layer in between two materials that either don’t like to bond, or undergo lots of different stresses. The first, and most important place for this is above your edges and underneath the first composite layer. Without this layer, all of the chattering and vibration that your edges see when they interact with the snow would likely cause the bond between the edge and the composite to break, tearing out your edge. You will also see rubber placed in the binding mounting area, to promote further bonding between the topsheet and top layer of composite. The second function of the rubber is for vibration dampening, which as you can guess from the description above, goes hand in hand with its “shear layer” characteristics.
LOWER COMPOSITE LAYER
We’ve arrived at the first of two of our composites layers, probably the easiest layer to modify and the hardest to understand. Your composites layers are comprised of fabrics (like fiberglass, carbon, aramid, Kevlar, etc.) with all of their pores and voids being saturated (and constrained) by epoxy. Composite fibers are most generally placed in one of 4 directions: 0° (parallel to the ski length), 90° (perpendicular to the ski length), and + or – 45° (though getting weaves at different angles is becoming easier and easier). 0° fibers give strength to the ski in the way that most people would think, longitudinally (think of the first way you always test a skis flex). 0° fibers help the most in wider skis in keeping the whole ski flat. With a lack of fibers in this direction, it’s likely that the ski can cup during production because of the heat changes and internal strain during the epoxy curing stage. + and – 45° fibers can be very useful, as they can aid in longitudinal stiffness, flatness, and torsional strength, as they have a portion of their strength going on both directions, parallel to the length of the ski, and perpendicular.
It should be noted that these composites layer would have no purpose if it wasn’t for the epoxy system used during the layup of the ski. The epoxy consists of a resin and a hardener which are mixed together just prior to layup and used to “glue” all of the layers together. All of the voids in the fiberglass must be filled to constrain the fibers after the epoxy hardens, and this constraint gives them their strength.
There are three main functions of your ski’s core: the first is to act as a spacer between the composites layers of the ski. The further apart these two composite layers are (or thicker the ski), the more effect they are going to have on the flex, and stiffer the ski will be. The second function of the core is to provide dampening, denser materials (hardwoods) will provide more dampening between the composites than a softwood or a foam. The third function is binding retention, which is why you will often see hardwoods under foot where the screws will be placed for your bindings. This is generally why cores are a mix of heavy and light woods, with the heavy, dense woods underfoot (ash, maple, oak, etc.), or at the center of the ski, and the light woods (poplar, aspen, paulownia, etc.) everywhere else to keep the mass down.
Sidewalls provide a number of functions, the most important two being waterproofing the ski, and second being providing impact durability. It’s argued that a full length sidewall ski provides better edge pressure in a turn over a cap ski, but in reality the amount of material over the edge is very similar, and probably not even a measurable factor for the average skier. In fact, sidewalls being what we might call a “dumb” material (meaning that it provides no flexural integrity to the ski, and really only weight), limiting the amount of sidewall in the ski is the biggest goal. One if its positive factors, waterproofing the ski, comes in to play because if the core simply extended through, it would be exposed to the elements. With sidewalls in its place, you have essentially encapsulated the entire core (which is susceptible to water damage) in an envelope of plastic, or non-permeable materials. The second is impact protection, as both fiberglass and your core aren’t very good with impacts, placing a sidewall material like UHMW-PE or ABS and absorb some of the impact, and possible give a more durable product. The alternative to sidewalls is a cap construction, in which the topsheet and fiberglass wrap around the edge of the core and terminate at the edge, still encapsulating the core as well. This construction is lighter, but can be perceived as cheap, as it doesn’t include any sidewall materials. We at Armada have chosen a hybrid sidewall/cap construction with our AR50 sidewalls, placing sidewall underfoot where you need it, and capping the nose and tail to keep swing weight down.
UPPER COMPOSITE LAYER
Most of the time this layer is the same or very similar to your lower composite layer so that there isn’t any warping or twisting due to different masses during curing. Generally, the upper composite layer will include some extra fiberglass underfoot (called a “binding mat”) to aid in screw retention.
Ah yes, the last stop on our trip and most definitely the prettiest. The topsheet mostly consists of a sublimation graphic (an image essentially baked in to the backside of the plastic), screen printed designs, or a combination of both. After the graphic is applied, the topsheet must be heat treated so that the pores are prepared for bonding. Then the plastic (generally a nylon, TPU, PE, or combination of the above) is placed as the final layer of our layup.
*Office Janitor and part-time ski designer Logan Imlach loves to work in overalls and is always up for working on his table tennis backhand – stop by and give him some reps if you’re driving I-80 between Park City and SLC.