Yarn Twist (S Twist - Z Twist), Twisting Process

Twist is simply the spiral arrangement of fibers around the axis of the yarn. Through twisting, the fibers are bound together and create a stronger yarn. The number of twists involved is normally referred to as turns per inch or turns per meter. Twisting, in yarn and rope production, process that binds fibers or yarns together in a continuous strand, accomplished in spinning or playing operations. The direction of the twist may be to the right, described as Z twist, or to the left, described as S twist. 

No matter the spinning system employed, all yarns contain twist to hold the fibers together. The frictional forces created by the twist are the means by which all yarns are held together. Most single yarns will be produced with a "Z" twist. That means the helix angel is the "Z" direction. Sometimes "S" yarns will be produced for special technical reasons. An "S" twist yarn’s helix angle is in the "S" direction. Because of its mechanical design, yarns produced on the OE system will always be "Z" twist yarns. Both ring and air-jet spinning systems can be set up to produce an "S" twist when it is required. 

Twist Multiple (TM): the ratio of turns of twist per inch to the square root of the yarn size in Ne. Twist multiple is a common way of designating how much twist a yarn contains. TM is a relationship between yarn number (or count) and the turns per inch in the yarn. Using number English or cotton count, that relationship is represented as follows: 

TM = TPI√ Ne. 

Where TM is twist multiple, TPI is turns per inch, and Ne is number English (or cotton count). Twist level may also be expressed in other ways, such as turns per meter. When communications between parties involve twist, it’s important to know the terms and units being used. 

S-Twist 

The fibers in the yarn form the center of the letter S, moving from lower right to upper left. This is caused from the direction the fibers are twisted into yarn. Also called reverse twist and left-hand twist. 

Z-Twist 

The fibers in the yarn form the center of the letter Z, moving from lower left to upper right. This is caused from the direction the fibers are twisted into yarn. Also called regular twist and right hand twist. 

Twist Multiple 

The ratio of turns of twist per inch to the square root of the yarn size in Ne. 

Turns Per Inch (TPI) 

The number of turns of twist in one inch of yarn. TM-twist multiple is derived from the TPI and the yarn count and describes the relative twist level in a yarn (TPI = TMvNe).