A polymer product for improving retention of hydrophobic internal sizing agents in manufacture of paper or board

A method for manufacturing paper or board is disclosed and further disclosed is an internal sizing system for providing improved retention of hydrophobic internal sizing agents. The internal sizing system includes a hydrophobic internal sizing agent as a first component selected from a group consisting of alkenyl succinic anhydride (ASA)， alkyl ketene dimer (AKD)， rosin sizes and any combination thereof， and a water-soluble polymer product including amphoteric polyacrylamide as a second component， which amphoteric polyacrylamide has neutral or cationic net charge at pH 7， a weight-average molecular weight of 700，000-18，000，000 g/mol and a total ionicity of 4-28 mol-%， where the first component and the second component are provided as separate components or as a combination of the first component and the second component.