than about 75 microns for example having an average diameter of from about 0 5 microns to about 50 microns or more particularly microfibers may have an average diameter of from about 2 microns to about 25 microns another frequently used expression of fiber diameter is denier which is defined as grams per 9000 meters of a fiber and may be calculated as fiber diameter in microns squared multiplied by the density in grams cc multiplied by 0 00707 a lower denier indicates a finer fiber and a higher denier indicates a thicker or heavier fiber for example the diameter of a polypropylene fiber given as 15 microns may be converted to denier by squaring multiplying the result by 0 89 g cc and multiplying by 0 00707 thus a 15 micron polypropylene fiber has a denier of about 1 42 15 2 u00d7 0 89 u00d7 0 00707 1 415 outside the united states the unit of measurement is more commonly the u201c tex u201d which is defined as the grams per kilometer of fiber tex may be calculated as denier 9 as used herein the term u201c spunbonded fibers u201d refers to small diameter fibers which are formed by extruding molten thermoplastic material as filaments from a plurality of fine usually circular capillaries of a spinneret with the diameter of the extruded filaments then being rapidly reduced as by for example in u s pat no 4 340 563 to appel et al and u s pat no 3 692 618 to dorschner et al u.