The diffusivity and solubility of cyclohexane in a high density polyethylene, HDPE, were studied using a gravimetric, quartz-spring, sorption balance. Solvent concentrations up to a weight fraction of 0.15 over a temperature range of 90 to 160 degrees C were measured. Diffusion coefficients in the range of 10-6 to 10-7 were determined. Two types of polymer samples were used: a commercial bead form and flat sheets prepared by melting the polymer. Within the experimental error no differences were observed between the two forms indicating that there were no significant effects caused by the melting and compression. The solubility of cyclohexane in the HDPE as a function of the activity of the cyclohexane was linear. Above the melt temperature the solubility data were predicted better by the group-contribution, lattice-fluid equation of state (GCLF-EoS) than by the van der Waals free-volume (UNIFAC-vdw-FV) model. Below the melt temperature a correction factor for the elasticity significantly improved the predictions for both models. Although the HDPE has a crystallinity of 77.6%, the experimental data and the Vrentas-Duda free-volume theory indicated no significant tortuosity effects. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012