dk,
See comments by Lee V., they`re worthless in junk waves.
Many years ago spoons were often shaped from surfboard blanks and then glassed, the deck scooped out and more glass added. Unfortunately they were high maintenance (weak in repeated compressive flex) ... soon forming point load stress "hingles", usually in the the rails, a precursor to complete breakage. To help resolve that ongoing problem, rather than surfboard foam, end-grain balsa (denser than surfboard foam) was placed in the rails. Very labor-intensive.
A much better idea is to build a female mold over a master shape. Then laminate the spoon inside that. An improvement is epoxy resin with many more layers of 4 oz. fiberglass and hand-pour high density polyurethane (10 to 12 lb./cu. ft. density) foam in the rails.
The best spoons... very strong in repeated compressive flex, resilient memory, sensitive, very light, made with high temp cure epoxy, carbon graphite and hand-pour high density polyurethane. End use for most flex spoons... uncrowded, long, higher quality waves.