An in situ bubble-stretching (ISBS) model has been proposed on the basis of an analysis of the dispersion process of inorganic additives in polymers. The ISBS model is applicable to a dispersion of solid granular aggregates in polymer melts because the dispersed phase itself serves as a nucleation agent, giving rise to bubbles that expand at the surface of the microgranules and their aggregates. In terms of bidirectional stretching, the ISBS process can increase the degrees of freedom of granule dispersion, which favors more homogeneous dispersion. According to theoretical predictions and indirect experimental estimations of the dispersion of nanoscale CaCO3 and nanoscale hydrotalcite in high-density polyethylene (HDPE), when the bubble expands, the stretching rate of the polymer melt on the bubble wall can reach 10(5)-10(6) s(-1). The field emission scanning electron microscopic images indicated that the granular size of dispersed CaCO3 and hydrotalcite in HDPE with the ISBS method is about 60-80 nm, two orders of magnitude smaller than that attained with a shearing rate of 103 s(-1) in a capillary rheometer. It is also predicted that elastic bubble oscillations may be generated through suitable control of process parameters and that their oscillatory frequency can be in the ultrasound range. This type of bubble oscillation can also promote dispersion. (C) 2003 Wiley Periodicals, Inc.