A 0.25m(3) laboratory repulper was built for the purpose of determining which variables (pulp type, rotor tip speed, pulp suspension temperature, rotor design, rotor to extraction plate clearance, power to vat volume ratio, and pulp suspension consistency) affect the specific energy (kW-h/ton) required for repulping. Scale replicas of 3 commercial repulper rotors were constructed to test the effect of rotor geometry on repulping specific energy. The pulp types used included kraft aspen, C-flute corrugated cardboard, office printing paper, and unbleached paper towel. The energy required for repulping was found to vary with pulp type, temperature, consistency, and rotor design. It was found that a given material at a given temperature and consistency requires a unique quantity of energy to be repulped independent of the rate of energy addition. It was also found that repulper rotors show Reynolds independence at rotor tip speeds greater than 12m/s. It was found that the specific energy consumption in a 0.25m(3) laboratory repulper was identical to that for a 15m(3) repulper given the comparison was made with identical pulp types, temperatures, consistencies, and rotor designs.