Lumberock® uses innovative extrusion technology to combine a mineral-fill compound with high-density polyethylene plastic. This formula allows us to manufacture solid non-porous dimensional profiles that are extremely durable and will not rot, crack, splinter or peel. Because no organic fills are used, there is nothing for mold or mildew to adhere to and nothing for water to decompose. Bacteria, insects and other organisms that thrive in areas with outdoor exposure and lots of moisture cannot permeate the surface of interior of the board. Lumberock® can endure prolonged submersion in saltwater and freshwater and is protected by our Limited Lifetime Warranty even in these conditions. Additionally, our board features increased strength and decreased thermal expansion due to our use of a mineral-fill additive