Paper fibers have a strong hydrophilic tendency because they contain a large number of hydroxyl groups that can form hydrogen bonds with water. When the paper is saturated with water it will lose most of its strength, this point is very suitable for toilet paper, corrugated core paper, but for most of the paper is not necessary, such as office paper, food boxes, cosmetic boxes, grocery bags of paper and so on. Sizing in the papermaking process is a method to improve the paper's resistance to water and liquids and to prevent the spreading and penetration of watery liquids.

There are two methods of sizing paper, one is in the paper before molding (pulping or batching) will be added to the sizing agent in the pulp, known as pulp sizing, the other is in the paper after molding coated on the surface of the paper or cardboard known as the surface of the release of glue. In addition to blotting paper, filter paper, wax paper, cigarette paper, household paper and other paper types, almost all paper need to be sized. Gluing of paper can improve the paper water resistance, oil resistance, resistance to printing ink and other properties, and at the same time can improve the smoothness of the paper, hydrophobicity, printing adaptability.