Everett's domain and Mualem's capillary-radii similarity models of hysteresis were used to characterize the moisture sorption equilibria of a bleached kraft paperboard of mean basis weight 230 g/m(2). The models predicted the experimental equilibrium moisture content (EMC) of the paperboard for the case of desorption scanning (similarity model only), adsorption scanning, spiral, and loop trajectories inside the main sorption hysteretic loop with good precision. Over an RH range of 15-90%, the root-mean-square deviation between the predicted and experimental EMCs was 0.11-0.83% (domain model) and 0.21-0.64% (similarity model). However, the similarity model is easier to use and requires data of only the two boundary isotherms that envelop the main hysteretic loop. The similarity method obviates the need of taking additional labor-intensive and time-consuming scanning curve data that is necessary to develop the moisture distribution function of the domain model and predicts higher-order EMC trajectories that lie inside the main hysteretic loop in a consistent fashion.