A screen filter is a single, thin layer of a material that has a symmetrical arrangement of openings or passages called pores. These pores trap all particles larger than the pore size on the surface of the filter. This process is called sieving, or size exclusion, and is the classic filtration method. It utilizes a rigid or flexible screen to separate sand and other fine particles out of water for irrigation or other applications. Typical screen materials include stainless steel (mesh), polypropylene, and nylon.