Z and S Twist Direction
topic
Z-twist fibres spiral from bottom-left to top-right (like the diagonal of Z); S-twist from bottom-right to top-left (like S). Z-twist is standard for single cotton yarns; S-twist is used in ply yarns where the folding twist is applied in the opposite direction to the single yarn twist for balanced structure. Twist direction is set by spindle rotation direction. Mixing Z and S twist singles in a woven fabric causes torque and diagonal distortion (bias).
Role
Twist direction knowledge is essential for fabric structure design. Using the wrong twist direction in woven or knitted fabrics causes dimensional instability, bias, and torque — defects that cannot be corrected in finishing. Understanding twist direction is the basis for designing balanced ply yarns and for specifying correct yarn to avoid fabric faults.