(3) the parameters should be physically significant; and (4) the effect of hysteresis should
be considered. The three-parameter model is generally preferred over two-parameter
models on the basis of these criteria. The third constant is added to the model to allow
its application over a wide range of aw values (up to 0.9) and temperature (Osborn et al.
1989; Schuchmann et al. 1990). In a three-parameter model, the first constant is a scale
factor for the overall capacity towards sorption of the material (especially at low aw values).
The second constant is an approximate measure of the isotherm shoulder, while the third
constant is a measure of the steepness of the slope over high aw regions (Schuchmann et
al. 1990)