PVP is divided into four levels based on its average molecular weight, and is commonly represented by K values. Different K values represent the corresponding range of average molecular weight of PVP. The K value is actually a characteristic value related to the relative viscosity of PVP aqueous solution, and viscosity is a physical quantity related to the molecular weight of polymers. Therefore, the K value can be used to characterize the average molecular weight of PVP. Usually, the larger the K value, the higher its viscosity and stronger its adhesion.