In a few cases, the fitting procedure completely fails or the obtained parameters are physically inexplicable. The predicted saturation uptake is in the order of a 1,000 mol kg -1 , or the heat of adsorption is a positive value. In those cases, the pure component isotherms were accurately described by the DSL model mathematically, however, thermodynamically, the parameters are not valid, and the fits cannot be trusted (see figure ). Generally, not every isotherm can be fitted to a DSL model, and assuming that in a set of pure component isotherms for different materials, all isotherms follow the DSL model, or any other model, can be erroneous.