AbstractMica and polystyrene in four ratios were sheared for three different times, each at three speeds, and at two temperatures in the viscoelastic region, in a screw mixer. From precise density measurements on the resulting composites, void volume fractions were calculated and found to be proportional to mica concentration and independent of total screw rotations. Experimental void/mica ratios were represented by a kinetic model; they decreased from a single value common to all conditions to a steady‐state value proportional to the square root of the screw speed. Void formation and elimination occur simultaneously. The goodness of the fit to the data is insensitive to the details of the kinetic model. The characteristic rate constant depends only on temperature, increasing at the same rate as the reciprocal of the low‐frequency dynamic viscosity. Cavitation in regions of diverging flow of the mixer may inhibit void elimination.