A method for improving holdout on a coated, cellulosic substrate, such as a man-made fiber board. The process comprises the steps of applying an aqueous carboxymethyl cellulose acetate butyrate size composition to a man-made fiber substrate, forming a sized substrate. The sized substrate is then dried. Next, an aqueous coating composition is applied to form a coated, sized substrate. The coated, sized substrate is then dried. According to the invention, the aqueous carboxymethyl cellulose acetate butyrate size composition used in the process comprises carboxymethyl cellulose acetate butyrate, water, and an organic solvent. The invention also relates to a sized, man-made fiber substrate comprising a man-made fiber substrate and a carboxymethyl cellulose acetate butyrate size. The carboxymethyl cellulose acetate butyrate may be either an internal sizing agent, or an external sizing agent.