We present a simple and yet effective method of producing asymmetric polymeric membranes. All it takes to prepare the membrane is to place a flat slab, which can absorb the solvent readily, on a polymer solution. The rapid absorption of the solvent by the slab leads to the formation of a thin dense skin layer and the presence of this top dense layer allows for the phase separation in the polymer solution to proceed beneath the layer. The solubility of a polymer in a solvent, as affected by solubility parameter and polymer molecular weight, determines the morphology of the membrane prepared by this controlled solvent absorption method. The preparation conditions can be tailored to produce "double-skinned" membranes and membranes with localized pore structure. (c) 2007 Elsevier B.V. All rights reserved.