opinion on 35 Cheoy Lee
Almost all boat builders core their decks with one of a number of materials. Probabaly the most common is end grain balsa. Balsa has a lot going for it. It is inexpensive, and has very good adhesion to the resin. It is very and good sheer and compression qualities. It conforms to fairly complex cruves and Balsa properly installed is quite durable. Of course there is the rub. Proper installation means complete bonding to the glass/resin laminates, sealing of all penetrations, and replacing high stress areas with non-compressible materials, typically marine plywood.
Another material used for coring is high density closed cell foams. High density foams are more expensive, harder to work with, not quite as sheer resistant as balsa, but will not rot even if allowed to get wet. It is really the best choice but because of expense it is pretty rarely used.
Lastly, there is plywood coring. Plywood coring is usually a misnomer. For the most part boats with plywood decks are actually built like a wooden boat except that the plywood is glassed over. In places were labor is cheap, this is the most inexpensive way to build a deck. It also provides a very sturdy substrate to fasten teak decks to. The problem with that is that each of the screws that fasten the deck enter the core and when the deck leaks moisture and air are present and so rot is just a matter of time.