Just finished this. The Red and blue outside part is probably some type of Polyurethane whilst the white part is Polyester judging by the smell when I turned it. It’s made from a Ten Pin Bowling ball. The outside was sanded to 1000 grit then polished, the inside is just sanded to 120 grit to leave a Matt finish. The inside looks and feels a lot like unglazed porcelain.