※ hole and curtain 1) Hole: It refers to the complete penetration of the surface of the paper, no holes in the fiber. Holes can be divided into pinholes, holes, and holes by size. 2) Curtain: It means that the fiber layer on the paper sheet is thin but not completely penetrated, and its light transmittance is larger than other parts of the paper sheet. The little ones are called light spots, and the big ones are called curtains.