Weft knitted fabrics tend to undergo certain dimensional change that causes distortion in which there is a tendency of the knitted loops to bend over, causing the wales to be at diagonal instead of perpendicular to the courses.

This is a very common problem in single jersey knits and it may exist in grey, washed or finished state and has an obvious influence on both the aesthetic and functional performance of knitwear. However, it does not appear more in interlock and rib knits because the wale on the face is counter balanced by a wale on the back.

Course spirality is a very common inherent problem in plain knitted fabrics. Some of the practical problems arising out of the loop spirality in knitted garments are: displacement or shifting of seams, mismatched patterns and sewing difficulties. These problems are often corrected by finishing steps such as setting/treatment with resins, heat and steam, so that wale lines are perpendicular to the course lines. Such setting is often not stable, and after repeated washing cycles, skewing of the wales normally re-occurs.

Evaluation of Spirality:

AATCC Test method 179 -2004:

This test method determines change in skewness in woven and knitted fabrics or twist in garments when subjected to repeated automatic laundering procedures commonly used in the home. Washing and drying procedures used for shrinkage tests and other home laundering tests are specified for this method.

For some fabrics the degree of twist of fabric in garments is not solely dependent on its behavior in the unsewn state; it also may be dependent on the manner of garment assembly.

This method is based on the following principle:

Change in skewness in fabric or twist in garment specimens resulting from procedures typical of home laundering practices is measured using bench marks applied to the specimens before laundering. Fabrics or garments that are distorted in their unlaundered state due to faulty finishing of the fabric or faulty assembly of garments may give deceptive results when laundered by any procedure. In such cases, it is recommended that specimens not be used, or if used, the results be considered as indicative of those specimens only.

One of the common methods of measurement of spirality in garment is indicated below:

Figure 1: Inverted T marking