flanges 125 and 126 at the ends thereof for attachment to the flash spinning device 90 and the collection section 150 respectively the open interior 122 has a generally circular cross section along its length through the nozzle section 120 and the interior 122 is larger at the exit end 132 than it is at the inlet end 131 the nozzle section preferably has a length of at least 1 5 times its diameter at the inlet end thereof and an internal contour that preferably diverges from the inlet to the outlet as will be described below the diverging contour is not necessarily continuous or always diverging but preferably does not include any portions with reducing diameter the open interior 122 includes a particular geometry which has two stages 135 and 140 the first stage 135 is generally cylindrical and extends for about 0 5 to 10 times the diameter thereof the diameter of the first stage 135 is preferably larger than the diameter of the tunnel 92 such that the fiber leaving the tunnel 92 34 sees 34 a step change in the diameter of the passageway from the spinneret 91 into the nozzle section 120 it should be noted that such a step change is preferably a 90 u00b0 step as illustrated in the drawing however it may be acceptable to arrange a step change such that the angle to the axis or centerline of the device may be considerably less than 90 degrees in other words the step may comprise a short portion that has a shape extending perhaps 45 u00b0 relative to axis of.