Abstract: The difference of the twist structure and properties in in-phase self-twist yarn and phased yarn is mainly discussed. There are three kinds of yarn zones: twist-twist zone, twist-zerotwist zone, zerotwist-zerotwist zone, existing in one cycle length of self-twist yarn. The existence of phase difference decreases the zerotwist length in yarn. When the phase difference (value c) is close or equal to the length of the twistless area (value b), the length of zerotwist-zerotwist zone obtain an minimum so that the best properties of self-twist yarn can be achieved. The test results of spun in-phase and phased self-twist yarn are accordance with the above conclusion.

Key words: self-twist , twist distribution , in-phase , phase , rubbing twist