Denim gets discussed as if the wash is the whole job. The wash is the visible part. The failures that make a run unsellable are usually happening in the fabric underneath it, and they have names.
Three of them cause most of the damage.
Shrinkage
Denim is woven under tension and it wants to relax. Add water and heat and it contracts, mostly in length.
Raw denim can lose four to ten percent. Sanforised denim, which has been pre-shrunk mechanically at the mill, loses one to three percent. Neither number is zero, and the second one still moves a 32-inch inseam.
What goes wrong. The pattern is cut to finished measurements rather than to measurements plus shrinkage. The garment is washed. It comes out short. Nobody notices until the whole run is done because the fit sample was made from a different fabric roll.
What to do. Get the shrinkage figure for the specific fabric lot, not the fabric type, and get it in both directions. Cut the pattern with that allowance built in. Then confirm it by washing a finished sample from production fabric, not from development fabric.
The two rolls behave differently and this is the single most common source of a run that measures wrong.
Skew
Skew is when the weft threads sit at an angle to the warp instead of at ninety degrees. The fabric arrives from the mill slightly parallelogram rather than rectangular.
What goes wrong. The pattern is cut on a fabric that looks square on the table. After washing, the fabric returns to its true angle and takes the garment with it. Pockets sit crooked. A back yoke tilts. The centre back seam drifts off vertical.
What to do. Ask whether the fabric has been skew-corrected at the mill, and by how much. Ask the factory to check the grain before cutting rather than assuming the roll is square. On a striped or heavily textured denim it shows up faster and matters more.
Twist, also called leg torque
The side seam of the leg spirals around the leg instead of running straight down it.
This is the twill weave doing what twill does. Denim is a diagonal weave and the yarns carry residual torque from spinning. Wash it and the fabric releases that energy by rotating. On a two-piece leg with a straight side seam, the rotation shows immediately.
What goes wrong. The seam that sat at the side of the leg on the sample ends up two inches forward after three washes. Customers notice and it reads as a manufacturing defect, because it is one.
What to do. Three routes, and they combine.
Use a fabric that has been mechanically de-torqued or one woven with balanced yarn twist. Ask the mill directly.
Build a counter-rotation into the pattern, deliberately setting the seam off-vertical so it lands vertical after washing. This is standard practice and a factory that has made denim before will already do it.
Wash a sample three times and measure the seam displacement at the hem. Anything past about half an inch is going to generate complaints.
What this means for approving a wash
A wash sample tells you about colour and hand. It only tells you about fit if it was made from production fabric, cut with the shrinkage allowance, and washed the same number of times the bulk will be.
The useful sequence:
- Confirm the fabric lot and get shrinkage, skew and torque figures for that lot.
- Cut the pre-production sample from that lot with the allowances built in.
- Wash it the full production recipe, not an approximation.
- Measure it against the tech pack after washing, not before.
- Wash it twice more and measure again.
What you approve at step five is what your customer receives. What you approve at step one is a swatch.
A note on stretch denim
Adding elastane changes all three behaviours and adds a fourth: growth. A stretch jean relaxes during wear and does not fully return, so it fits differently at hour eight than at hour one.
That is not a defect and it is what customers expect from stretch denim, but the amount varies enormously with the elastane content and the recovery quality. Test it by wearing the sample for a full day rather than by measuring it flat.
The specification that prevents most of this
Name the fabric by mill and article number, state the required shrinkage tolerance in both directions, state the maximum acceptable leg twist after three washes, and state that the pre-production sample must come from the production lot.
Four lines. They remove most of the risk in a denim run.
Tirarin is a custom denim manufacturer working in your wash, your fit and your fabric weight, with the sample setting the standard for every pair in the run.
