Abstract: By controlling the design and operational parameters in accordance with particular relationships fibers having an average diameter of 7 microns or less can be formed by passing molten material through orifices in a peripheral wall of a rotor without using conventional hot gas blast attenuation externally of the rotor. The primary fibers are broken into finite lengths to produce staple fiber by a plurality of relatively cool and relatively low pressure air streams which are circumferentially spaced about the rotor and which flow in a direction transverse to the direction of travel of the primary fibers as they exit the orifices in the rotor. The rotors utilized in the perferred embodiment of the present invention have a peripheral wall with at least 40,000 orifices having diameters of about 18 mils or less.