Experiments show that migration of dialkyldiketene on neutrally sized paper is possible. Attempts to prove that a chemical reaction occurs between dialkyldiketene and cellulose yielding a beta-ketoester bond failed; whereas, an ester bond of cellulose modified with stearoylchloride has been identified. The excellent sizing efficacy of dialkyldiketene derivatives with a nonreactive functionality, obtained by opening the lactone ring, leads to the conclusion that the cellulose reactivity is not the determining factor for neutral sizing agents. This is in contrast to what has been suggested in the literature over the past 25 years. -- AATA