Core wood selection
Quotes are verbatim and attributed to their original authors.
Almost any straight-grained wood can make a ski core; the differences are in weight, stiffness, and how easy the stock is to find clean. Poplar and aspen are the default, with harder woods for stringers and lighter woods for weight savings.
The workhorses: poplar and aspen
Poplar has the favoured balance of low weight and good stiffness, and aspen is nearly identical. The real difficulty is sourcing it knot-free — but knots are less fatal than beginners fear:
Where clean boards are scarce, builders finger-joint around the knots or switch species — spruce and fir have "virtually identical properties" to each other and work well (chrismp); pine tends to be sappy and knotty; birch is light but "a lot of tearout using a planer… even with sharp blades" (Dr. Delam).
Stringers and reinforcement
Softer field wood is combined with harder stringers — maple or ash along the edges and under the binding-insert zone — for screw hold and edge durability. Dense tropical woods double as sidewalls (see Sidewalls).
Lightweight cores: paulownia and balsa
Very light woods cut weight but drink resin, so builders pre-seal them:
The payoff is real: one builder's paulownia-cored ski came out "~9 oz lighter than the same ski with my traditional core" with a very similar flex (vinman). A thin brushed coat of epoxy, scraped and lightly sanded, is enough to partly seal the pores without stopping the bond.