Abstract: Systems and methods for the manufacture of reinforced, three-zone, microporous phase inversion membrane having any one of a plurality of different possible pore sizes in any of the three zones from at least a single mother dope batch is disclosed. The systems and methods include formulating at least a single mother batch of dope in a vessel preferably maximizing the non-solvent to solvent ratio for a given weight percentage of polymer for use in a microporous phase inversion membrane production operation to produce three-zone phase inversion membranes having one of a plurality of different predetermined pore sizes in any or all of the three zones. The at least one mother dope batch is controllably formulated in at least one vessel such that the temperature of the dope does not exceed a predetermined maximum mixing temperature and is maintained at a relatively low temperature (lower than the mixing temperature) suitable for storage.