A method for reducing the permeation rate of a permeable species through a polymeric material includes identifying a solubility-increasing species in the polymeric material having a reversible affinity for the permeable species, and removing or altering at least a portion of the solubility-increasing species in the polymeric material. In one application, the permeable species is water, and the solubility-increasing species is hygroscopic. A example of a polymeric material is an elastomeric polymer. The solubility-increasing species may be removed in part from an existing piece of the polymeric material by leaching it out. The polymeric material may instead be manufactured with a reduced content of the solubility-increasing species.