Coosa Composites Nautical 15 Panel. Typically used as a semi-structural component this premier panel is a high density, closed-cell polyurethane foam and continuous strand fiberglass that can be utilized in multiple applications. Similar to Bluewater 20, without the woven roving, results in a slightly lower strength but is much more economical. Does not attract mold or fungus and offers a very low water absorption of 1.5 percent or less. Density is 15 pounds per cubic foot and is 61 percent lighter than plywood.