Hagedorn's poly boards meet all the requirements for a material that is strong, flexible, resistant to environmental degradation and very slippery. Our full-length boards and flush-head fasteners make a smooth, obstruction-free surface for easy unloading. Individual tongue & groove boards make an almost watertight box and, in the event of damage, are easy and inexpensive to replace. Being plastic (high-density polyethylene), the boards expand and contract with temperature changes. Our frame design and bolting procedure allow the boards to expand and contract freely without undue stress to either boards or frame.