This question is posted in a discussion by one of the readers:
Spirality is a dimensional distortion in circular knitted fabric. Spirality is bad as it leads to displacement of seams and mismatched patterns. It can also leads to sewing difficulties. The major cause of spirality is the twist in roving and yarn. To minimize spirality, Z-twist yarns should be knotted on clockwise rotating machine and S-twist yarns on counter clockwise rotating machines. Tighter Fabics exhibit less spirality compared to looser fabrics which means that finer gauge machines will reduce spirality.
It can also be reduced by setting the twist either by autoclave treatment, yarn dyeing or using balanced plied yarns.
For more information SITRA has a nice Technical brief here
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