Filter paper filtration not only has the function of a screen but also has the function of deep filtration; the side magnification shows that the filter paper is a multi-layer structure. The front of the filter paper should face the direction of airflow, the screen surface should be in the direction of the gas flow. Color lines are drawn on the screen surface to facilitate user identification and prevent mistakes; if the front and back directions are wrong, the filter element is in use, and dust is stored. Ability is reduced by 30%. http://www.fypackingpaper.com/cellophane-paper/