Phase separation spinning, a method originally reported by Zwick [1], has been used to produce porous polypropylene fibers by spinning a solution of polypropylene in naphthalene and subsequently extracting the naphthalene with diethyl ether. In phase separation spinning, a hot solution is spun into cool air where the temperature drops below the solubility limit so that the polymer precipitates during spinning. If a relatively nonvolatile solvent in the proper concentration range is used, two continuous phases are formed. Extraction of the nonvolatile solvent produces continuous voids to form a porous fiber.