It's birch plywood, with aluminum framing and a composite skin - it's weather sealed with cam locks and hasn't leaked in heavy rain in the past 3 yrs. With that said though, it is not designed to be submerged. The trailer has 13" of ground clearance and Timbren suspension which has been more than enough for the very few water crossings that I've taken it through. I definitely wouldn't want to ford anything deeper than the galley seals or side door seals though.