In sizing, the strength and printability of paper is increased. Sizing also improves the hydrophilic character, liquid spreading, and affinity for ink. Starch is the most common sizing agent.  Cationic starch and hydrophilic agents are also applied, including alkenyl succinic anhydride (ASA) and alkyl ketene dimers (AKD).
Cationic starch increases strength because it binds to the anionic paper fibers. The amount added is usually between ten and thirty pounds per ton. When starch exceeds the amount the fibers can bind to, it causes foaming in the production process as well as decreased retention and drainage.