Single, or one-ply, yarns are single strands composed of fibers held together by:
at least a small amount of twist
filaments grouped together either with or without twist
narrow strips of material
single man-made filaments extruded in sufficient thickness for use alone as yarn (monofilaments).
single yarns of the spun type, composed of many short fibers, require twist to hold them together and may be made with either S-twist or z-twist. Single yarns are used to make teh greatest variety of fabrics.