Novel assembly of composite fibers

An assembly of fibers composed of at least two dissimilar fiber-forming polymers, characterized by the fact that (1) it consists of numerous fibers, (2) at least 90% of said fibers have a non-circular cross-sectional shape, (3) the cross sections of at least 50% of said fibers differ from each other in at least one of shape and size, and (4) at least 50% of said fibers each have in their cross section taken at right angles to the fiber axis at least two side-by-side coalesced blocks of at least two dissimilar fiber-forming polymer phases with at least a part thereof being exposed to the peripheral surface of the fiber, at least one of the number, shape and size of the blocks varying from fiber to fiber. The assembly of fibers can be produced by extruding a molten macroblend composed of many molten phases of at least two dissimilar fiber-forming polymers through a mesh spinneret having many small openings; and taking up the extrudates from the small openings while cooling them by supplying a cooling fluid to the extrusion surface of said spinneret or to its neighborhood, whereby said extrudates are converted into numerous separated fine fibrous streams and solidified; characterized in that said macroblend is prepared by coalescing many distinct molten phases of at least two dissimilar polymers in such a manner that in a phantom cross section of the molten macroblend taken parallel to the spinneret, there exist many effective continuous boundary lines between the molten phases of dissimilar polymers each of which lines has a length larger than one-fourth of the length of a partitioning member which defines one small opening in the spinneret, whereby said many boundary lines are cut with the partitioning members in the spinneret.