A theoretical model is proposed to describe the exfoliation process of clays in polymer melt flows. It shows that exfoliation is a function of shear rate, viscosity of the matrix, the Hamaker constant, overlapped fraction, gallery spacing, and aspect ratio. The stress ratios (i.e., stretching stress/van der Waals' stress) are significantly dependent on the orientation of the connector vector. Tactoids with more clay layers can be broken more easily. The predictions of the model appear to be in harmony with experimental observations reported in the literature. (C) 2004 Society of Plastics Engineers.