The objective of the study reported here is to demonstrate that it is possible to manipulate membrane porosity, pore size, and permeability through the choice of extractant and drying conditions in the thermally induced phase separation (TIPS) process for making microporous membranes, To do so, ten different extractants were used to remove mineral oil from polyethylene films and two different evaporation conditions were used to remove the extractant and produce microporous membranes. The dimensions, microstructure, and permeability of the membranes were used to measure the impact of extractant choice and drying conditions on the membrane morphology. The solubility parameter was used to represent the affinity between the extractant and the polymer. Boiling point was used to represent the volatility of the extractant and therefore, the kinetics of extractant removal. Surface tension was used to represent the force exerted by the extractant on the solid matrix as the extractant is removed from the membrane. Each of these properties was related to the membrane morphology.