A process and apparatus is disclosed for forming fibers from attenuable materials, such as molten glass, by attenuating streams of glass from the bottom of a bushing wherein the bottom has downwardly presented wall portions at upper and lower levels. According to the disclosure the upper or lower wall portions are formed into series of bosses, each having a multiplicity of orifices in the lower ball portions. Bosses with alveoles are disclosed. Filamentary material is manufactured by drawing at least one filament from each boss independently of each other boss or from separate fiber forming regions in each boss regardless of whether or not the material has flooded the bottom surface of any boss. Embodiments with one alveole per boss or plural alveoles per boss are disclosed. Where plural alveoles per boss are provided, shallow transverse grooves in the lower wall portions of the bosses may be used to separate the orifices of one alveole from the orifices of adjacent alveoles. Controlled cooling permits the selective drawing of one or a plurality of filaments from each alveole.