another embodiment the fiber is conveyed directly to a high speed windup operating at a linear rate 500 times preferably 1000 times greater than the linear rate of extrusion thereof the maximum achievable ssf is a function of polymer melt viscosity which is in turn a function of temperature and polymer mfr obtaining a ssf of greater than 1000 can be problematic when using low temperatures and or low mfr materials due to fiber breakage during spinning however under such conditions it has been found that ssfs less than 1000 are sufficient to obtain high strength and low shrinkage in a particularly surprising aspect of the process of the invention it is found that the melting point of the fiber depends upon a spin factor f s defined according to the formula where the shear rate is the actual shear rate to which the molten polymer is subject in the extrusion aperture and ssf is the actual ssf employed spinning fibers of mfr of about 1 to about 6 g 10 min can present a particular problem since it may be difficult to achieve a ssf of greater than 1000 at a temperature below the onset of thermal degradation ca 400 u00b0 c for the most preferred polymers however it is found surprisingly in the practice of this invention that the desirable features of low linear density high strength and low shrinkage.