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SYNOPSISThe accurate measurement of water vapor sorption and permeation in polymers is complicated because water has a tendency to adsorb on high energy surfaces, a relatively high heat of vaporization, and a high solubility in most polymers. These issues and the difficulties they cause in the design of sorption and permeation equipment are reviewed. Some new approaches to circumvent these problems are described. Data for bisphenol A polysulfone films are used to illustrate these approaches. 0 1996 John Wiley & Sons, Inc. I NTRO DU CTlO NWater vapor sorption and permeation characteristics of polymers are important for many industries, such as wastewater treatment, gaslair dehydration, pharmaceuticals, and packaging. Accurate measurement of these properties is complicated, however, by the ability of water to hydrogen bond and its high cohesive energy, which create special problems in the design of equipment to determine them. This article reviews these issues and offers another set of approaches to the design and operation of sorption and permeation facilities.The systems described here for water vapor sorption and permeation measurements were constructed for the study of miscible blends of a relatively hydrophobic polymer with a hydrophilic polymer. The polymer pair employed in the first phase of this work is bisphenol A polysulfone, PSF, and poly(viny1 pyrrolidone), PVP, which are miscible over the entire composition range. Detailed results for this blend system will be reported subsequently.Results for PSF films are used in this article to illustrate the issues involved in the design of equipment for sorption and permeation measurements.