Inverse Gas Chromatography was utilized to examine the interaction of water vapor with the surfaces of a polyimide homopolymer and poly(imide-siloxane) random-block copolymers of increasing siloxane content. The studies employed 45-60 meter, thin-polymer-film mega-bore capillary columns to maximize surface area. The free energies of specific surface interaction with water and the dispersive components of the solid surface free energies were determined. An increase in the polymer siloxane content from 0-wt% to 10-wt% resulted in a decrease of approximately 4 kJ/mol in the free energy of water-specific surface interaction. A further increase in siloxane content to 30-wt% was not found to increase surface water resistance significantly. Dispersive components of the solid surface free energies of the copolymers were comparable to values reported for poly(dimethylsiloxane) homopolymer.