Twist per inch

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T.P.I. - Twists per inch is a term used in the textile industry. It is the number of twists inserted to yarn per inch. This value varies from count to count and depends upon the factors: - the yarn count, - staple length of fibre

It is calculated as:

TPI= T.M. * $\sqrt(Count)$

Where, T.M.-Twist multiplier or K (twist factor)

Twist factor has been established by experiments and practice that the maximum strength of a yarn is obtained for a definite value of K. In the case of ring-spun cotton yarns, for example, the following values of K have been found to give the best results.

  Warp yarns, 35's and less      4.75
  Warp yarns, 35's to 80's       4.50
  Warp yarns, 80's to 110's      4.25
  Filling yarns, medium numbers  3.50

Filling yarns usually have a lower twist factor because strength is not so important and appearance is more important.Ply yarns frequently have twist factors of 4 to 6,while crepe yarns are often two or three time ordinary yarns.