Detailed results are presented on the absorption and desorption of water vapour (0-100% r.h., 30-90 degrees Celsius) by cellulose triacetate, secondary cellulose acetate, ethyl cellulose, drawn nylon 6.6 yarn, Terylene, Orlon, wool and Fibrolane. The sorption characteristics of the samples were stabilized prior to the sorption measurements by means of several absorption-desorption cycles at 90 degrees Celsius. The sorption results are analyzed, discussed and compared where possible with the results of previous workers. The isoteric heats and entropies of sorption are derived and discussed briefly.