Abstract: An apparatus is provided for predicting the extrusion performance of a thermoplastic resinous polymer, which includes at least three and preferably four capillaries arranged in series with each successive capillary having a larger passageway than that of the immediately preceding capillary and with each capillary having substantially the same ratio of passageway length to cross-sectional area. The apparatus also includes a pump for forcing a heated polymer melt through the capillaries at a constant volumetric flow rate, a sensor for measuring the temperature of the polymer melt, a sensor for measuring the pressure drop of the polymer across each capillary, and a combination recorder and processor for determining the polymer viscosity in each capillary (different shear rates), whereby the extrusion performance of the polymer can be predicted. A method for predicting extrusion performance of a thermoplastic resinous utilizing these polymer capillaries is also provided.