Black mask to distinguish anyway and solid white, solid color without printing mask similar, the direction of the folds on the mask is where you can judge, three folds of the mask in the correct wearing of the folds downward direction is the outside, there are also four folds of the mask, propped up after the middle of the piece protruding outward is the outside. In addition, when the mask is opened, the top two folds are facing upward and the bottom two folds are facing downward. You can also judge the positive and negative by the depth of the color of the mask, when worn correctly the outside color will be darker, the inside color is lighter, the mask’s print is usually on the outside, when worn correctly the print can be seen by everyone. More important is the metal strip, the protruding side is the outside and the flat side is the inside.