Why do T-shirt side seams twist after washing?

Short answer: Side seam twisting is called spirality or torque. It mostly comes from the fabric: single jersey knitted on circular machines tends to have wales that are not perfectly vertical, and the twist in the yarn wants to relax, so the fabric skews when washing releases stresses. If the fabric is finished without correcting this skew, or panels are cut off-grain, the garment twists after washing. Ways to reduce it include using lower-twist or balanced yarns, fabric finishing that sets the fabric straight, compacting, cutting on grain and checking skew before cutting. ISO 16322-3 gives methods to measure spirality of knitted garments after domestic laundering, and the standard notes that garments from circular knitted fabrics can have inherent nonverticality of wale alignment.

Causes

• Yarn twist and twist liveliness in single jersey.
• Circular knitting creating inherent skew.
• Fabric finishing that does not correct skew.
• Cutting panels off-grain.
• Washing releasing stresses.

Ways to reduce it

• Choose yarns with suitable twist for knitting.
• Ask the mill for skew control in finishing and compacting.
• Check fabric skew before cutting and cut on grain.
• Consider fabric structures less prone to spirality.
• Use tubular or side-seamless construction carefully, since it can show twist more.

Testing

• Measure garment spirality after washing with ISO 16322-3, which uses ISO 6330 laundering.
• Measure dimensional change with ISO 5077.
• Compare results with an agreed limit in the specification.

Production checks

• Check fabric skew on each roll or lot.
• Check marker and cutting alignment.

A worked example

For the shirts in the question, measure spirality on washed pieces with ISO 16322-3 and check fabric skew on retained rolls. If fabric skew is high, ask the mill to adjust finishing; if fabric is straight, check cutting. Retest before bulk.

Specifying limits

Include a maximum spirality percentage after a stated wash procedure in the fabric and garment specification, and agree it with the mill and factory.

Design choices

Some designs make twist more visible. Stripes, contrast side panels and long body lengths show any skew clearly, while relaxed fits and darker plain colours hide it better. If a design is sensitive, set a tighter spirality limit for that style.

What the standard measures

ISO 16322-3 marks reference lines on the garment, launders it with ISO 6330 procedures and expresses spirality as the sideways displacement as a percentage of a marked distance. It offers different procedures, and the standard notes that results from different procedures might not be comparable, so state the procedure in your specification.

Limits

Some spirality is inherent in single jersey. Aim to control it within agreed limits.

Facts, recommendations and uncertainty

Established: side seam twist is spirality from yarn twist, circular knitting and finishing, and ISO 16322-3 measures it after laundering. Recommendation: control yarn, finishing and cutting and set a spirality limit. Uncertain: the right limit for each fabric.

Sources and further reading

• ISO 16322-3:2021 — Spirality after laundering: woven and knitted garments
• ISO 6330:2021 — Domestic washing and drying procedures for textile testing
• ISO 5077:2007 — Determination of dimensional change in washing and drying

Standards and regulations are referenced by their published scope. Test parameters, cycles and pass levels should be agreed with your laboratory for the specific product; legal requirements should be confirmed for each destination market.