Die swell reduction is observed as a result of filler incorporation into polymer matrix. The degree of die swell decrease depends among others on filler particles geometry. In the paper results of experimental investigations concerning relations between particle geometry and die swell are presented for polyethylene and polystyrene filled with a number of commercial fillers. Approximation functions describing these relations were developed This enabled simultaneous analysis of the influence of different particle geometry properties on die swell. Good fitting of approximation models to experimental results was achieved. Similar behavior of polyethylene and polystyrene compounds was observed. Shape ratio exhibited the most pronounced influence on die swell. The higher is the shape ratio of filler particles the smaller is die swell. Much less significant influence showed specific surface and mean particle diameter.