Snowboard Design & Construction Part 3: The Structural Layers
Welcome to the third instalment of our snowboard design and construction series. After discussing snowboard basics like shape and profile in part one and then wood cores in part two, it's now time to move onto the structural layers.
If the core is the filling in the sandwich construction than the structural layers are the bread. Structural layers are generally formed by combining glass fibre strands in a variety of weights and densities with some kind of matrix. This combination creates a rigid layer that adds longitudinal and torsional strength to the board, or to put it plainly, "you make the board stiffer by adding stiff fibreglass layers".
Structural Layers
We're going to concentrate primarily on talking about fibreglass, as pretty much all boards use fibreglass structural layers. However, on some top-end boards, the glass layer is replaced by carbon fibre, but no matter if the structural layers are glass or carbon, the same mechanical properties apply to the material, it's just that the carbon is going to be more powerful.
Glassfibre
Glassfibre has excellent strength in both tension and compression, but across its axis, it's really weak. To overcome this weakness, fibres are orientated in multiple layers to create a sheet matting that prevents the fibres buckling, forming a material that is strong in multiple directions.
For snowboards, these multidirectional fibres are stitched together rather than woven. What this means is that you have a layer of fibres running in one direction, and then a second or third layer running in alternative directions. These are then stitched together, creating a sheet material.
This manufacturing technique creates matting that is less prone to damage during the construction process, ensuring a more consistent performance for the board.
Resins
To turn that floppy sheet of glass fibre fabric into a rigid structural layer and help bond it to the rest of the board, you need to add a matrix. The matrix is usually a thermosetting resin that when cured forms into a hard plastic material, bonding together with the glass fibres to create a rigid and strong structural layer.
Now, this bit is probably irrelevant to most people, but hey, if we're going to go into detail lets go into detail.
On snowboards, you've generally got three types of resin that form the structural matrix. These are epoxy, polyurethane and eco-resin. These three resins all have different properties, so when the designers create the board, these properties have to be taken into account.
Epoxy & Polyurethane Resins
Epoxy resins were the traditional resin that pretty much everyone used to use. Epoxy resin cures very hard, so that has to be taken into account during the design stages because it's going to create a stiffer overall flex. However, the downsides of epoxy are pretty significant. The first is that it's really toxic, the second is that it's prone to a chemical reaction that can affect its performance, and that's why over the past few years you've seen almost a wholesale shift towards using polyurethane resins.
Polyurethane resins are less toxic and more stable. They also remain more flexible when cured, allowing the designer to be a lot more accurate when creating the boards' flex
Eco-resin
The final resin is what we're going to call eco-resin. Different brands use different names for these, but in reality, they're all pretty similar. Eco-resins are a group of Polymer resins that are non-toxic and usually based on vegetable extracts (i.e. sap). Bio-resins are similar to polyurethane resins in that they don't cure as rigid as epoxy so this has to be taken into account when designing the board. The benefits of bio-resin though are so obvious at both an environmental level and staff welfare level, so that's why we see bio-resins become far more commonplace in snowboard construction.
Fibre orientation
So, we now know how manufacturers create the structural layers, lets have a look at how they use them to give the board different flex characteristics. We're going to focus on the different fibre orientations that manufacturers use. These have the same mechanical characteristics no matter the glass weight or density; it's just that the heavier and denser fibres are going to create a stiffer flex.
Bi-ax
As you can see from the image, bi-ax glass features glass running in two directions at 0° and 90°. These add strength along both the length and the width of the board. However, because the reinforcing is only running across the length and the width, it's not adding much resistance to torsional twisting, and that's the reason that you see bi-ax glass used on boards that have a softer or more playful flex.
By reducing torsional rigidity, you're going to allow the board to twist, creating a predictable and easier ride. This allows the board to absorb terrain undulations allowing the rider to concentrate on riding rather than worrying about what's going on under their feet, creating the perfect flex for beginners or for park and urban riders who need that predictable feel.
However, the downside to bi-ax glass comes when you start to put load into it. Because it's not very powerful torsionally, it's really easy to overload the flex as you start to ride faster and harder. As you start to drive the board, the softer flex just can't hold the energy that you're putting into it, so it reaches a point where it says no more and just lets go. You'll generally notice this when you're riding faster, you'll feel the board starting to wash out in the final third of the turn. It's kind of like over winding a spring, at some point the flex just can say I can't hold this any longer and let go. To counter that, you then step up to tri-ax glass.
Tri-ax
If you compare the images, you can see that we've got the same glass running at 90°, but now we've added two glass layers with the fibres orientated at angles across the width.
By running those additional fibres at opposing angles across the width, we've added resistance to torsional twisting giving the board a responsive and dynamic ride. This stiffer torsional flex allows the board to hold more energy creating a stable ride at speed and a more powerful overall feel.
One of the great things about tri-ax glass is that you can also manipulate the torsional flex by altering the angle of those glass strands. So, if you're after a super-responsive ride, you run the angles at 45°. This is the optimum angle for tri-ax. If you go over 45°, it loses torsional rigidity. You can also shallow off the angle to around 33° giving you a slightly softer torsional flex. You'll normally see this in the higher end freestyle boards where you need performance but performance with a more predictable feel. As with the 45° glass, you wouldn't want to go much below this angle because again you’re going to lose torsional rigidity. In fact, go much below 30° and you're really just turning it into a bi-ax glass.
Reinforcing layers: Materials
Now that we know how structural layers work, let's take a look at what we call the reinforcing layers. Designers use these to add an extra level of performance into the board. However, first we need to look at the materials that manufacturers utilise to extract that extra performance.
Until quite recently, this material was pretty much exclusively carbon fibre, but over the past few years, we've seen more and more boards moving to basalt.
Carbon fibres
The starting point for carbon fibre is the raw material called the precursor. The precursor is usually made from poly-acrylo-nitrile but can sometimes be either Rayon or Petroleum Pitch. All of these materials are organic polymers categorised by long strands of molecules bonded together by carbon atoms.
The precursor goes through a process where it's drawn into long thin fibres; these fibres are then heated to between 2000 and 3000° centigrade in a pressurised oxygen-free furnace. This process causes noncarbon atoms to vibrate and detach themselves from the fibre. The remaining carbon atoms then bond together to form a tight crystalline structure that attaches parallel to the long axis of the fibre. These fibres are then bundled together to form what we call a tow i.e. carbon fibre.
Because of that unique atomic bonding process, you get a lightweight material that delivers high stiffness and high tensile strength, making it perfect for snowboard construction. However, the downside of that complex manufacturing process means that carbon fibre is really expensive.
Now because of that prohibitive cost alongside its not exactly environmentally friendly construction process, we've started to see many brands move towards using reinforcing layers formed from basalt fibres.
Basalt fibres
Basalt is an igneous rock, which means it began in a molten state. You can find basalt rock in just about every country in the world, so it's readily available. To turn this rock into a fibre is a relatively straightforward process compared to carbon fibre.
First, the quarried basalt rock is crushed into a fine material; this material is then placed into a melting bath which is heated to around 1500° Celsius in a furnace to turn the rock back into a liquid form. The liquid rock is then extruded through a series of dies forming a continuous strand of fibre. There are no additives, no complex pressurised heating; it's just that raw molten rock extruded into a fibre. Now, as with the carbon fibre, the single strands are then bundled together to create the useable basalt fibre.
These bundled fibres are then laid up in exactly the same way as carbon fibre. When mixed with the matrix during the board's layup, the basalt fibres show an increased strength of around 13.7% over traditional glassfibre.
Although the basalt's increased strength and stiffness don't rival those of carbon fibre, it still makes it perfect for snowboards, because on the majority of boards you're only looking for a little bit of stiffness to improve the performance. Using carbon fibre in these circumstances would not only be a bit overkill, but it would also significantly increase the price of the board.
Reinforcing layers: The Lay Up
Unlike the main structural layers, carbon and basalt are generally used as a collection of fibres running in a single direction as opposed to a sheet material running multiple fibres in multiple directions. Laying up the reinforcing this way allows the designers to add stiffness and enhanced flex in a very controlled manner. Let's now take a look how board designers use reinforcing in different zones of the board to enhance specific riding characteristics.
Beam
As you can see from the image, the beam runs up through the centre of the board. This increases resistance through the length creating a snappier and more lively flex. The more beams you add, the more power you get. This configuration is going to give the board more pop, so it's perfect for boards that want a lively feel through the length but still wants to retain a more predictable torsional flex.
X-bracing
As you can see from the image, it's pretty obvious as to why it's called X-bracing. X-braces can be added to either the tip and tail of the board individually or to both at the same time. This layout creates stiffer torsional zones at the tip and tail of the board by reinforcing the torsional stiffness in those areas. These prevent the tips twisting giving the board a more dynamic response into and out of the turn whilst allowing the centre part of the board to remain a bit more predictable through the middle of the turn.
Cross bracing
Again this reinforcing configuration runs in an X format, but this time the stingers run from the contact points in the nose to the opposing contact points in the tail. As you can see from the image, this reinforcing runs across the whole width of the board, so what this is going to do is increase the torsional resistance giving the board a more stable and reassuring ride. However, it's going to beef up that torsional flex without having to resort to a lot stiffer overall structural layers and compromising some of the more rider-friendly characteristics of those more easier going boards.
Beam Variation
As you can see, this is a variation of the beam lay up. However, instead of running a single beam through the centre of the board, this configuration runs a beam either side of the insert pack. These beams can again be formed from single stringers through to multiple and wide format stringers depending on how much power you want to add. The advantage of running this format is that not only does it increase the pop through the length of the board, it also adds power to the sidecut, the closer you move the beams to the edge of the board. This gives a more powerful and stable ride though the turn and is particularly suited to faster riders who need the security of an increased edge hold.
Forks
Forks generally run from under the insert pack out to either the contact points or though to the tail. You normally see this format on more freestyle focused boards where you're looking for pop at the tips but you still want to retain a more playful and predictable overall ride.
Combination
The final configuration is simply a combination of all or some of the other lay ups. You’ll only really find this on high-end boards that are looking for maximum control and response in all areas.
Other possible materials
It's also worth mentioning a couple of other materials that you’ll see cropping up when it comes to structural layers. These are Kevlar and Flax.
Kevlar
Contrary to opinion Kevlar isn’t there to increase the strength of the board, it’s there to act as a dampener. By integrating Kevlar into the glass structural layers, you get a marked improvement in dampening. This creates a board that is smoother and generally more comfortable to ride over a full day. This dampening isn’t so relevant for regular boards but on high-end boards that are stiffer it can help reduce high-frequency vibrations that come up through the board and can cause foot pain and fatigue.
Flax
Flax is a material that we’ve seen gain a bit more popularity over the past few years. As with basalt, Flax is a natural material, being extracted from the stem of the Linseed plant. Flax fibres are formed on the outside of the stem of the plant giving them a natural resistance to loading and bending. It’s these properties that allow Flax to be integrated into the boards structural layers. Flax fibres are usually mixed with the glass, cutting down on the environmental impact of regular glassfibre. Flax also has excellent dampening properties, so we are also seeing it being integrated into the boards top sheet structure.
Stay tuned for the final instalment of this series covering everything you need to know about snowboard bases. All parts are also available on your YouTube channel.
