Co-extrusion produces a fence profile made of two layers. As you might expect, it requires a larger investment by manufacturers: an investment in equipment, tools, training, and more. However, it does cost less than mono-extrusion when it comes to material prices. The two layers are chemically attached through great pressure and high temperatures, so that they forge a molecular bond and cannot be separated. Co-extrusion does not produce a laminate- or veneer-like product, as some opponents claim; the outer layer is quite thick, and two layers are very securely bonded together.