Process variables affecting the deflaking or defibering kinetics of recovered papers in repulping to produce molded pulp were investigated with laboratory low and high consistency pulpers and a pilot high consistency pulper. The defibering kinetics at various repulping conditions were compared in terms of the deflaking rate coefficient, which can be easily obtained by measuring flake contents as a function of slushing time and then by performing a non-linear regression analysis on the data. The two main variables affecting defibering rate are found to be the repulping concentration and the rotational speed of rotor, which have to be chosen as manipulated variables to optimize a repulping process. Increasing repulping concentration and rotor speed generally promotes the defibering of recovered paper.