Abstract: Flat filaments have a flatness (A/B) of 7 to 25, where A is a length of at least one of the two longer sides of a substantially rectangular, transverse cross-section of each filament and B is a length of at least one of the two shorter sides of the substantially rectangular, transverse cross-section of each filament. The flat filaments also have a fineness of 0.5 to 40 denier, and are provided on each of the two longer sides with one or more ribs continuously extending in a direction of an axis of the filament and having a width W and a height H. The number of the ribs on each longer side ranges from 1 to A/2W, the rib width W ranges from B/2 to 3B, and the rib height H ranges from B/2 to 2B. The filaments have excellent nontackiness and bulkiness and permit easy elimination of crimps by polishing, and can be suitably used as raw fibers which, when formed into a pile product, provide the pile product not only with a soft feeling but also with resilient and substantial feeling.

Abstract: The present invention relates to acrylic fibers each having a Y-type cross section which consist of an acrylic polymer constituted of at least 50% by weight of acrylonitrile, characterized in that the Y-type cross section is constructed substantially of three rectangles and when the thickness values of the middle part, innermost part, and outermost part of each component rectangle are represented by d.sub.0, d.sub.1, and d.sub.2, respectively, the ratios of d.sub.1 /d.sub.0 and d.sub.2 /d.sub.0 are each in the range of 0.95 to 1.05, and a process for producing the same comprising discharging an organic solvent solution which contains an acrylic polymer constituted of at least 50% by weight of acrylonitrile, dissolved at a concentration of 22 to 30% by weight, and has a viscosity of 200 to 500 poises, through spinneret holes each having a Y-type cross section constructed substantially of three rectangles, into a coagulating liuqid composed of an organic solvent and water at a spinning draft of 1.1 to 1.