a method for making a skinless essentially symmetrical hydrophobic polysulfone microporous membrane by the steps of forming a casting solution containing a dissolved polyethersulfone polymer , a solvent for the polyethersulfone polymer , and a lower aliphatic glycol ; coating a substrate with the casting composition ; exposing the coated substrate to atmospheric conditions ; passing the exposed coated substrate into a precipitation bath to precipitate the membrane , the precipitation bath containing a lower aliphatic glycol and water ; rinsing the membrane ; and drying the membrane .