The core is the most important part of a ski, in my opinion. There is some debate in the world of ski building whether a ski’s core or its composites should contribute the majority of a ski’s stiffness and flex pattern. Composites are much stiffer than the core for the weight they add, but a ski that relies too much on composites just can’t provide the same feel and damping. So what are the advantages and disadvantages of different types of core materials and which will keep your pow-covered mustache smiling all day long?

Wood Cores In the grander scheme of things, wood can be rather expensive depending on its quality. To save on cost, most manufacturers buy lesser-quality wood (typically in shorter sections or with knots); then try to improve its properties superficially. Wood can also have some really funky grain patterns and discontinuities that often lead to questionable flex patterns. Though most high-end ski manufacturers will flex all the skis they make and pair only the skis equal in stiffness and flex, most inexpensive skis don’t get this special treatment. Problems like improper grain orientation or bad finger joints will often negatively affect how a ski performs on snow.

To minimize the effects of these anisotropic properties, the wood is cut into long skinny strips and then laminated together across the width of the ski. Because it's also more expensive to buy long strips of wood, most wooden cores are also held together by finger joints along the length of the ski. Finger joints are just what they sound like: small interlocking areas at the tip of each strip of wood. They need to be carefully placed so that they don’t fall next to each other and form a weak point in the ski. While it seems scary that there would be small strips and joints in the core of a ski, the effects of these shortcuts are negligible when done right.

Wood for ski cores needs to have a high stiffness to density ratio and for this reason, poplar is a popular (see what I did there?) species for the job. Aspen is a close cousin of poplar and is often employed because it sounds cooler. Often times, stringers of a stiffer wood (like maple or hickory) are used in places to augment the flex pattern of a ski despite their increased weight. These more dense hardwoods are typically used sparingly, however, because they can add as much as 50-percent more weight for a given amount of stiffness. Another benefit of having two different types of wood in the same core is the damping that it provides. Because species of different stiffness are going to want to resonate at different natural frequencies, lots of chatter and vibration can be canceled out.

Some companies will use softwood species like pine to cut additional cost, but it can cause problems with durability and binding screw retention. Recently, bamboo has been all the rage in ski building circles and many tout it as a green alternative to hardwoods. While it does provide an interesting and desirable pop, a whole lot of epoxy is needed to hold the short bamboo fibers together. When you start adding more nasty petroleum-based epoxy (which is needed to hold the layers together anyways) bamboo’s fast-growing, “sustainable” benefits become questionable at best. Some companies are exploring soy-based epoxies, but no large scale manufacturers have made the switch yet.

Foam Cores
The main benefit of a foam core is its low cost and light weight. The material itself is fairly cheap, and it rarely requires processing. Foam is also easier to cut and shape than wood which lends itself to skis with a 3D geometry in order to cut even more weight while retaining stiffness. Though most foam cores are cut from a larger sheet of foam, some cores are also injected into an existing cavity and allowed to fill the desired shape and harden. Because it is composed mostly of air, foam is also used often in touring skis where light weight is most needed and also sometimes with skis for beginners where a low swing weight is desirable.

While these qualities can be beneficial in some skis, there are some significant downsides to using foam cores as well. Most foams can’t reach nearly the stiffness wood has and because of that, many foam skis rely more on composites and have a very different feel to them because of it. The increased use of composites can cause skis to vibrate more, especially at high speeds. Also, foam doesn’t have directional fibers like wood, so it doesn’t transmit force as well, which results in a less lively ski. Most foam also fatigues much quicker and more significantly than wood. This means that a robust ski in November can be a total noodle by the time April rolls around.

In the end, it’s a matter of personal preference. If you’re looking for a heavy duty stiff board to rail on and you can sacrifice on weight, wood ought to be your weapon of choice. If you’re looking to log a few thousand feet of vertical each time you head out, but won’t be laying down the hammer 24/7 with reckless abandon, then perhaps foam will suit your needs. No matter which poison you pick, you’ll be that much more educated the next time you pull the trigger on a shiny new pair of boards.