XPS (Extruded Polystyrene) insulation is a rigid, closed-cell form of insulation. XPS insulation is manufactured using an extrusion process. This means that the products are melted together and then the liquid is shaped by a die. It expands as it cools. The result is a product with a closed-cell structure which prevents water penetration. Also, the manufacturing process produces a strong and durable insulation board that has high compressive strengths. This makes XPS insulation a great choice for flat roof and ceiling insulation boards.