Side seams that twist after washing are a common single jersey problem. The fabric is knitted in a tube, and the yarn twist and the knitting structure can make the loops lean, which is called spirality. If the fabric is finished in a way that holds it straight temporarily, washing releases it and the panels skew. Because the side seams are sewn along the cut panels, they follow the fabric and move around the body.

Measure skew after washing

AATCC TM179 measures skew change in fabrics and garments after home laundering. ASTM D3882 covers measuring bow and skew in woven and knitted fabrics. Ask the mill and the factory to use one named method and to report results after washing, not only on the fabric roll. A fabric that looks straight on the cutting table can still twist badly after the first wash.

Where it can be controlled

At the mill, spirality can be reduced through yarn choice, including yarn twist, knitting settings and finishing that sets the fabric properly rather than just straightening it. Some buyers use open-width finishing for this reason. At the factory, cutting matters too. Panels should be cut along the true direction of the courses and wales, and spreading tension should not distort the fabric before cutting.

What to specify

Set a maximum skew after washing, tied to the named method, the wash procedure such as ISO 6330, and the number of cycles. Include it in fabric approval and in the pre-production sample check. If the tee has a printed or embroidered front, also check that the graphic stays centred after washing, since twisting can pull it off-centre.

Some side-seam movement may be acceptable for a relaxed style, but it should be a measured, agreed amount rather than whatever the fabric happens to do. Tubular tees without side seams can still twist; the twist just shows in the hem and the print position instead.

Keep the washed reference tees from approval as a visual standard alongside the measured result. Record the skew figure by fabric lot, so a change in yarn supplier or finishing route shows up as a number rather than as customer complaints months later.