The twist direction of the yarns used in the weaving of the fabric can be in two ways: “S üküm or“ Z üküm. The reason for assigning these yarns to the yarn twists is related to the centerline of the letters S or Z. This line shape in the letters coincides with the direction of the fibers extending along the yarn.

If the twist of a sewing thread or knitting thread is unwound, it can be seen that the twist in the ply yarn is in the opposite direction to the twist in the single yarn. This twist direction allows this to make a balanced yarn with less inclination to form twist or twist.

Fabrics woven with spun yarns generally have “Z” twist in the warp direction and “S” twist in the weft direction. The light is reflected in opposite directions with respect to the twist direction of the yarns. Based on this feature of the twists, “Z” and “S” twisted yarns are used in the warp in order to create lines with different brightness in the fabric.

For physical tests performed in accredited laboratories, standards issued by local and foreign organizations are complied with. In this context, twisting (from yarn) work is based on the following standards:

• TS EN ISO 2061 Textile - Twist determination of yarns - Direct counting method
• ASTM D1422 Standard test method for twist in single twisted yarns by twisted-untwisted method
• ASTM D1423 Standard test method for twisting yarns with direct counting

In the laboratories, measurements are made using yarn twist test equipment. These instruments make the twist measurements of single and double ply yarns and the “S” and “Z” twist can be selected on the device and high precision results are obtained.

All laboratories need to use state-of-the-art equipment and equipment in order to achieve fast, quality and reliable results. It is also important that they have an experienced and trained staff as well as a strong technological infrastructure.