Super-Pro DE Filter Grids are constructed with a special reinforced center tube which creates a duct to funnel water from the outer most edges of the grid into the center and through the entire frame. All of our grids are made with a high performance woven polypropylene that contains only virgin resins to assure the highest strength and to maximize filtration. Seams are stitched by our product team experts with a chemical resistant heavy 4 ply thread.