Skew in denim is the condition where the weft yarns run at an angle to the selvedge instead of at right angles to it, and torque is the twisting of a garment, most visibly the leg of a pair of jeans, that appears after washing when a skewed or unbalanced fabric relaxes. Both arise from the twill weave itself, because the diagonal line of a 3/1 twill puts an unbalanced stress into the fabric that tries to release when the fabric is wetted.
Mills control this by deliberately skewing the fabric in the opposite direction during finishing, so that after washing the fabric settles close to square. A buyer should specify a skew limit and a leg twist limit and test both.
Where skew comes from and how mills correct it
In a right-hand twill woven from Z-twist yarn, the yarn twist and the twill line work in the same direction, and the fabric tends to rotate when it relaxes. Left-hand twill, broken twill and balanced constructions reduce this tendency, which is why broken twill was developed for workwear trousers. Loom settings, uneven tension across the width and poor stenter alignment can add skew of their own.
Skew is measured as the displacement of a weft yarn across a given width, expressed as a percentage or as an angle. Before finishing, a standard twill denim may show several percent of natural skew.
On the finishing range the fabric passes through a skewing unit, usually a pair of angled rollers or a bowed roller, that pushes the weft out of square by a controlled amount in the opposite direction to the natural movement. The fabric then goes through sanforising, which sets it. After the garment is washed, the built-in skew and the natural skew cancel and the leg hangs straight.
The amount of skew to add depends on the construction, the weight and the wash the garment will receive, so mills usually finish each quality to a known target rather than to a single rule. A stretch denim needs different settings from a rigid one because the elastane recovers in the weft.
Testing and acceptable limits
- Fabric skew is tested to ISO 13015 or AATCC 179, before and after a defined wash.
- Garment torque, or leg twist, is tested to AATCC 179 or the brand's own method by measuring the shift of the side seam after washing.
- Typical fabric limits after wash are around 3 to 5 percent, and leg twist limits are often around 3 to 5 percent of the leg length or a fixed figure in centimetres, depending on the brand.
- Results depend on the wash programme, so the test conditions should match the garment wash.
What to specify
State the maximum skew after wash, the maximum leg twist on the finished garment, the test methods and the wash programme. Ask the mill for its skew finishing target for the quality you are buying and check it against the garment maker's experience with similar fabrics. If leg twist appears in bulk, the fault may lie in the fabric, in cutting off grain, or in sewing, so keep fabric test records to settle the matter.
How we help
We audit finishing ranges and skew control during mill visits, send sealed samples to an NABL-accredited lab for skew and dimensional change under your wash programme, and supervise loading. You get weekly updates, one approved supplier plus one backup, and a free 20-minute sourcing review to start.