Adjust the size and tightness before wearing, so that the hat can't move freely on the head, and you can't feel that the hat shell must be connected with the hat lining. At the same time, the two should not stick together. There must be a certain gap, the chin strap must be fastened, the chin strap should be close to the chin, and the chin should be relaxed and restrained, but I feel that it should be worn properly to adapt and the hat strap should be tightened. The size should be adjusted according to the wearer's head shape. Finally, check the air tightness of the mask, cover your mouth and nose and exhale. If you feel air leaking from it, adjust it appropriately. Wear it correctly, tighten the headband and adjust the size according to the wearer's head shape.