Abstract: The formation and stability of foams within sizing pastes used in warp sizing operations are discussed through analyzing the mechanism of the foam formation.The causes for forming foams are surveyed from three aspects: size,size mixing and sizing.With respect to the size,surfactants,protein,and partially hydrolyzed PVA components,as well as some chemical additives and neutralized agents,and improper viscosity and pH value are often the direct cause of formation of foams.The mechanism of foam elimination by antifoaming agents is discussed and some commonly used antifoaming agents are briefly introduced.