Extrusion coating with polyethylene (PE) is a widely used process for applying a thin, continuous layer of molten plastic onto a substrate such as paper, paperboard, aluminum foil, or plastic films. The goal is to enhance barrier properties, sealability, strength, and surface characteristics in a cost‑effective way.In a typical extrusion coating line, polyethylene granules are fed into an extruder, where they are melted and homogenized by a rotating screw under controlled temperature and pressure. The molten PE is then forced through a flat die, forming a thin, uniform curtain of polymer. This curtain is directed onto a moving web of substrate that is precisely guided through the coating station.The substrate and the molten polyethylene meet at a chill roll nip. The chill roll, usually a large, water‑cooled metal cylinder, rapidly cools the polymer, solidifying it and bonding it to the substrate. Nip pressure, line speed, melt temperature, and air gap (the distance between die and nip) are key process parameters. By adjusting these, operators can control coating thickness, adhesion, appearance, and mechanical performance.Different grades of polyethylene are selected according to the final application. Low‑density polyethylene (LDPE) is commonly used for its good sealability, flexibility, and clarity. Linear low‑density polyethylene (LLDPE) offers improved toughness and puncture resistance. High‑density polyethylene (HDPE) may be chosen when stiffness and higher temperature resistance are required. Blends and tie‑layer resins can be used to improve adhesion to difficult substrates or to tailor barrier properties.Extrusion coating provides several functional benefits. It can create a moisture barrier for paper and paperboard packaging used in food, liquid, and frozen applications. It can enhance heat‑seal performance in flexible packaging structures. When applied to aluminum foil or specific films, PE layers contribute to better handling, reduced pinholing, and improved mechanical strength. The process also enables the production of multi‑layer laminates in a single pass by combining coextrusion technology with lamination.Process control and quality assurance are critical. Thickness is typically monitored using on‑line gauging systems, while adhesion, seal strength, and coefficient of friction are tested off‑line. Surface treatment, such as corona discharge on the substrate or the PE surface, may be used to improve printability and lamination performance.Environmental and sustainability aspects are increasingly important. Extrusion coating with recyclable polyethylene grades supports the development of mono‑material packaging structures that are easier to recycle. Efforts are also made to optimize material usage, reduce waste, and incorporate recycled PE where technically feasible, without compromising performance.Overall, extrusion coating with polyethylene is a versatile technology that combines efficiency, flexibility, and robust performance, making it indispensable in modern packaging and industrial applications.