Twist
Also searched as: yarn twist, S twist, Z twist, twists per meter, TPM, turns per inch, TPI, twist multiplier, twist factor, ply twist
Twist is the helical rotation of fibers or filaments around a yarn's axis, stated as turns per unit length plus a direction (S or Z), that holds staple fibers together.
In detail
Twist converts a loose strand of short fibers into a coherent yarn: when the yarn is pulled, the helically arranged fibers press inward on one another, and the resulting friction resists slippage. Direction is named by matching the slope of the surface fibers to the central stroke of a letter: fibers that follow the diagonal of a Z give Z twist, and those that follow an S give S twist. Twist level is quoted as turns per meter (tpm) or per inch (tpi). Plied yarns are usually twisted opposite to their singles, which balances torque and reduces snarling.
The science and numbers
Finer yarns need more turns to reach the same surface helix angle, so twist is normalized with a multiplier. In metric terms the multiplier equals tpm multiplied by the square root of (tex divided by 1000), which is the same as tpm divided by the square root of metric count. In the English cotton-count convention, tpi equals the multiplier times the square root of Ne, and typical multipliers are roughly 3.0 to 3.6 for weft and knitting yarns, about 3.8 to 4.5 for warp yarns, and above 5 for crepe yarns. Twist is measured by untwisting a specimen of known length, either directly or by an untwist and retwist method.
A practical example
A knitter notices that a single Z-twisted yarn makes a jersey swatch that skews diagonally after washing, because the yarn's residual torque relaxes. Two of those singles are then plied together with S twist, giving a balanced two-ply yarn, and the new swatch stays square. The fiber and overall thickness are similar; the twist architecture is what changed.
What to distinguish
More twist is not always better. Strength rises with twist only up to an optimum, after which fibers lie too obliquely to carry load efficiently, and high twist also makes yarn harder, less bulky and more lively. A twist figure means little without the yarn's linear density, which is why twist multipliers are used. Continuous-filament yarns need little or no twist to hold together.
Origins and history
Twist direction is one of the first features recorded when a textile fragment is analyzed, because spinners in different traditions tended to favor one direction, so S or Z spin can hint at technique and origin. The letter convention is convenient because it does not depend on which end of the yarn the observer holds: a helix has the same handedness viewed from either end, so any two observers describe a given yarn the same way.
Related terms
Sources & further reading
- Textile School: Twist multiplier to TPI and TPM calculator
- Textile Learner: Yarn twist, types, factors and measuring methods
- Service Thread: Industrial multifilament yarns and importance of twist
Technical references reviewed 2026-09-22. Examples are illustrative. Industry organizations and manufacturers describe their own fields; their references are not independent product endorsements. Figures are approximate and depend on the stated test conditions.