Wood and Foam
These are the two primary materials now used for the core of a ski. Wood cores (more durable than foam) are composed of long vertical strips of laminated wood. These strips maintain their flexibility and give a lightweight material to layer other materials over.
The composite layers go above and below the wood or foam core. Fibers such as fiberglass, Kevlar, carbon or boron are layered in several directions for strength.
Plastic is used for the ski base, sidewalls and tops of skis. Base sheeting is ultra-high molecular-weight polyethylene plastic that absorbs wax well. P-tex or polyethylene is traditionally used on the tops of the skis where graphics are displayed.
The edges that are so important to carving turns on skis are made of steel runners and are attached to the base with epoxy. Aluminum or titanium may be used occasionally in an ultralight ski.
Rubber or Cork
Other materials act as shocks for skis, such as soft rubber or cork. They are sometimes inserted along the sidewalls to help absorb shock and enable better flex.
As mentioned above, epoxy is a key ingredient in skis. It is used to stick nearly everything together and bond the entire piece of gear. Epoxy is composed of resin and hardener, which is extra-strong when it when bonds and dries.