Abstract: A model in fuzzy mathematics was proposed to describe the structure ofan amorphous polymer. On the basis of the structural model, the authors believed that there are more microcavities in a rubbery polymer than in a glassy polymer and hole filling is an important sorption mechanism both above and below the glass-transition temperature. Furthermore, the authors assumed that in an amorphous polymer there are two types of voids with different interactions on penetrants. A generalized sorption model based on the above assumption and molecular thermodynamics was developed which incorporated both the successful daul-mode model below the glass-transition temperature and Henrys law above it. The model parameters can be interpreted on the molecular level.