Ideas concerning the use of a flat slot die with rollers in the technology of extrusion foaming of polymers are developed. Based on the experimental study of low-density polyethylene foaming with isobutane, dependences of the cell density and foam density on the polymer solution viscosity, gap width between rollers, die temperature, and talc concentration have been analyzed. A model is formulated for estimating the intensity of coalescence of supercritical bubbles in an inhomogeneous field of flow velocities. The number density of supercritical nuclei formed in a polymer-gas solution in the limiting case of high pressure drop rate is estimated. The obtained simple estimations allow the results of experiments to be justified on a qualitative level. (C) 2015 Society of Plastics Engineers