Sizing is used to help make paper less absorbent. This means it can resist water damage, and it won’t soak up ink, water colors and the like when in use. There are two kinds of sizing, internal and surface. Internal sizing is added to the pulp during the papermaking process. Surface sizing is added at the end of the process. Depending upon the desired results, sizing agents range from natural substances such as starch, rosin and gelatin to chemical substances such as Alkyl Ketene Dimer (AKD), Styrene-Butadiene Latex (SBL) or Alkenyl Succinic Anhydride (ASA).