I haven't torn mine up yet (1994 220BR), but I'm certain it's epoxy-painted marine plywood. We have boats that just missed out on the fiberglass floors. If my bilge is any indication, my floors are a dull blue-gray epoxy paint under the carpet. Not as pretty as the white fiberglass surfaces of newer boats. The carpeted sides will also be the same color under the carpet (but will be the fiberglass hull, not ply). That's the main thing keeping me from ripping my carpet out. I'd still have the carpet on the sides, or I'd have to rip it ALL out and to a lot of painting to get it all looking sharp.