Owing to the twist, all or some of the fibers take up the required helical disposition. The number of fibers affected by the twist, and the degree of winding, are strongly dependent upon the spinning process. In ring-spun yarns, twisting takes place from the outside inwards. At the periphery (the outer sheath A, Fig. 52), owing to the greater degree of winding, the fibers have a lesser inclination, (γ = angle between the fibers and the axis of the yarn) than in the interior of the yarn (the core B). Since the fibers become steadily less tightly wound towards the core, ring-spun yarn may be said to have sheath-twist. Under loading, the outer layers will tend to take the radial forces and the inner layers will tend to take the axial forces. However, by increasing pressure inwards, the radial forces reinforce axial resistance to sliding apart of the fibers.
Accordingly, fully twisted yarns with sheath-twist have high tensile strength but are not so resistant to abrasion. Under abrasion the outer, highly tensioned fibers are destroyed. Since these fibers hold the yarn together, the strand loses its cohesion. Hairiness on the yarn surface is mainly caused by protruding shorter fibers.