Measurements of the water self-diffusion coefficient were made for a set of nine commercially available contact lens hydrogels, both at equilibrium water content (EWC) and as a function of reduced water content, using the pulsed field gradient NMR method. The data were shown to lie approximately on a universal curve, suggesting that water content (WC) itself was the predominant factor in determining the water diffusion coefficient. However, fitting of the data tr, a specific binding model suggested that subtle differences in the diffusional behaviour existed between the materials. These differences were measured in terms of the proportion of specifically bound water (p(wb)). It was shown that the calculated proportions could be correlated with the EWC, and that they agreed reasonably well with the proportion of nonfreezing water measured for similar materials using DSC.