AbstractThe Phenomenon of draw resonance and the cyclic size fluctuation of an extruded shpae are related to basic changes in the “melt strength” (force per average cross‐sectional area required to draw the molten fiber down under fixed conditions). Melt strength values are obtained by a modified rheometer which consists of a vertical chamber to melt and hold the polymers at 190–250°C, a piston for extrusion, a take‐up system, a strain gauge to measure the drawdown force and a recorder for continuous force‐time plots. Melt strength increases with take‐off speed but not proportionally. At higher velocities, draw resonance is apparent through a sinusoidal‐like variation in fiber diameter. The amplitudes of melt strength and diameter waves are correlated with molecular weight, melt viscosity, swell, melt temperature and