Filter paper is a semi-permeable paper barrier placed perpendicular to a liquid or air flow. It is used to separate fine substances from liquids or air. Filter paper comes in various porosities and grades depending on the applications it is meant for. The important parameters are wet strength, porosity, particle retention, flow rate, compatibility, efficiency and capacity.Qualitative filter papers are what most users would consider general purpose filter papers. There are a vast range of applications in and out of the laboratory. Composed of cellulose fiber, these filters are manufactured from high-quality cotton linters treated to maximize alpha cellulose.