A ski is a ski. It has a base. It has its edges. It has its topsheet with a Norwegian explorer staring up at you (well, the best ones do, anyway). And when you’re choosing a ski, you compare specs. You read about the base; you look at the geometry, the rocker, the taper; you read about the core and the rare composite materials that go into the ski’s construction.
One thing few of us do, however, is think about the sidewalls – which is a pity. These are an often-overlooked but interesting element of ski design, and integral to any ski’s construction and performance.
What are sidewalls?
The sidewall is a strip of dense plastic incorporated into the ski construction. It sits between ski core and topsheet along the ski’s length, over the edges of the sole.
Its primary purpose is to prevent damage to the ski core, maintaining the ski’s overall integrity. If you end up in a tangle of limbs and skis falling foul of a steep and icy snowmobile track, it’s the sidewall that prevents the steel edge of one ski from exposing the wooden core of the other along the side. Likewise, if you drop your skis on the ground or hit a stump shedding speed in a forest, the core will remain undamaged when the sidewall takes the brunt.
ABS-sidewalls
Many skis made in “sandwich” or “semi-cap” construction have ABS sidewalls. This is acrylonitrile-butadiene styrene – a type of thermoplastic that’s become the standard in good skis. It offers good stability, it protects against water penetration, and protects your sides from wear and stray steel edges.
ABS sidewalls are associated with higher costs for ski manufacturers. But they add many desirable properties. Since this type of sidewall is highly strong and dense, it confers the ski torsional stiffness and better edge grip.
Torsional stability is resistance to twisting and bending – a positive attribute when switching from edge to edge, initiating a turn, or edging your skis to carve or shed speed with control.
Skis with ABS sidewalls have better characteristics when driven hard, on edge, than skis without. They’re also more resistant to damage, water penetration and easier to repair should you damage the steel edge – even if the skis are somewhat heavier and more expensive to produce.
ABS sidewalls.
Photo: Crister Næss v/ Åsnes
The three different kinds of sidewall construction
Today, it’s reasonable to say that factory-made skis come with three different types of sidewall construction. The difference between them is a question of how much of the ski is covered along the length. As we’ve seen, the ski’s sidewall determines its torsional rigidity – its willingness to twist and bend from edge to edge. Having a ski with high torsional stiffness is an asset when you’re edging your skis. It’s about control.
A good sidewall mitigates edge compression. Imagine a dent at the edge of your base caused by, say, stomping hard on a concealed tree stump. The base of your ski is compressed in that spot, no longer flat. The dent has bent the sidewall up so far that the edge of the ski is distorted. Perhaps the topsheet has even come free. This is edge compression. It can be staved off by the density of an adequate sidewall, preventing the ski from over-bending and the core losing its integrity in that spot..
The sidewall took one for the team here – and for “team”, read “core”: you can repair a sidewall, but you usually can’t repair a core. Repairing a dent may be a question of fixing the steel edge, patching what needs to be patched, gluing what needs to be glued, and using heat and pressure to return everything to where it ought to be.
There is a downside to dense sidewalls, however; they add to the ski’s weight. Design philosophy is a matter of finding a compromise between feel, function, durability, agility and weight. These are the same compromises we consider when we choose a new pair for ourselves.
“Sandwich” construction
Skis with sandwich construction have the greatest torsional rigidity, longevity, and ruggedness. The entire sidewall is buttressed, making it hardy and resistant to twisting from edge to edge.
This construction works really well for all types of skis – assuming other design elements are thoughtful, it can contribute to a consistent feel, consistent control, and dependable bite in tougher conditions.
Another advantage of sandwich construction is that the entire core is protected. This is an advantage if you ever go out skiing on your skis. Which you should, if you’ve spent money on skis. When we go skiing, we fall; we hit concealed boulders; cold hands drop skis; steel edges go astray; things shake about in the roofbox.
The disadvantage of sandwich construction is that the side walls are relatively heavy. If sheer performance is your priority, a full sandwich sidewall might not be necessary.
Cap construction
Where the sandwich construction is all about covering and buttressing along the ski’s edge, in a cap construction ski, there’s nothing there other than the topsheet . Think “marzipan on a cake” sealing the contents, in this case shrunk to the core, down along the walls to the steel edge and sole. This results in a slimmer appearance, perhaps more rounded, depending on the kind of ski.
Obviously, constructed without ABS, this makes for a lighter ski. And for some of us (ski-mo racers, weight fetishists and endurance-oriented tourers among us) this might be a desirable design choice. The designers themselves, however, have to find other solutions for strengthening the core – the choice of wood and the construction, chiefly.
Capped skis are not, necessarily, the most stable at speed. Skis designed for edging at speed with dependable control in varying conditions are frequently constructed differently. But it isn’t all or nothing, and there are a number of good and well-thought-out skis on the market with a capped construction where the compromise is worth it.
This was a popular design choice for years. Designers are turning to other solutions now that the weight of sidewalls has decreased, and the ski industry has finally understood that weight isn’t everything. The pleasure of the descent, for which stability and control are key, is pretty fundamental..
Semi-cap construction
It probably isn’t difficult to work out what semi-cap construction entails: the design aims to exploit the advantages of both cap and sandwich with a partially-covered core buttressing the ski’s effective edge.
In a semi-capped construction, the skis’s midriff is covered: the area where stress and wear are concentrated. It is also a section of the ski significantly affecting its performance when one is edging. Leaving tips and tail with a cap construction, sealed by the topsheet alone, semi-cap design permits weight savings and torsional stiffness where it’s required: the effective edge. Theoretically, the ski is sufficiently solid, comparatively light, with adequate control at speed. Modern skis, designed with a lot of rocker and taper, exploit this compromise with their softer, more forgiving, tips.
A semi-cap construction has consequences, both in robustness, of course, but also in agility. If you’re used to using the full length of the skis to drive a turn, for example, or sloughing some extra speed in a turn you’ve already initiated, say, then this can be demanding on the skier’s technique. The tip might not be as torsionally stiff as you would like – but these sorts of things are problems for very technical skiers and skis made specifically for harder conditions.
It is, as always, a question of compromisee.
Not certain which bindings choose for cross-country skiing in the backcounty? Confused by the difference between NNN-BC or 75mm bindings? Cable-curious? Find all the answers here!
Skins are more than a strip of carpet with glue on the back. They’re tools designed to help us in pursuit of pristine snow, perfect lines, and/or solitude. Something this magical demands a proper description of how it’s made.
If you’re going to mount bindings on cross-country skis built for breaking trail, you have a choice. You can let professionals do it for you and avoid water damage to the wooden core, screws sitting proud of the holes or crooked bindings… or you can bid farewell to your warranty cover, prepare the polyurethane glue and drill, and read on…
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