Congratulations on purchasing what I consider to be one of the finest small blue water cruisers ever built, and one of only thirty. It is neither foam nor plywood. Mine (#6) has an interior of what is apparently resin and microballoons. I've had my L28 since 1978 and wouldn't trade her for any other boat. Seakindly, nice motion, fairly weatherly and speedy. Pretty much across the board, the 28's will do 8.4 knots. Since I left out the inboard and filled and faired the prop aperture, she does 10.4 knots. No kidding.