Containing 92 percent or more by weight of acrylonitrile units with filaments numbering fewer than 70,000 (+/-2000) with filament diameter 1.59 decitex (plus or minus 0.027) or less, or in a separable tow construction capable of being separated into tows of 70,000 (+/-2000) or fewer with filament diameter 1.59 decitex (plus or minus 0.027) or less.