How denim fabric is made
Denim is a warp-faced twill. The warp yarn is dyed with indigo before weaving, either as ropes of yarn dipped and oxidised many times (rope dyeing) or as a sheet on a slasher range. Indigo stays mostly on the yarn surface and leaves the core white, which is what lets denim fade when washed. The weft is usually undyed, so the back of the fabric is pale. Stretch denim adds elastane, usually as a core-spun weft.
After weaving, the fabric is singed, may be coated or mercerised, and is usually skewed and sanforised. Skewing pulls the twill lines to an angle that offsets the twist the fabric develops in washing, and sanforising shrinks it mechanically so residual shrinkage stays within the spec. Both decide how the finished jeans will behave.
Ahmedabad, listed by DGFT as a Town of Export Excellence for textiles, is home to many of India's large denim mills, according to Apparel Resources (5 September 2024). Mills sell to jeans makers in India and abroad; for the garment side, see denim jeans inspection.
What we check on denim fabric
| Check | How it is checked | What fails |
|---|---|---|
| Shade grouping | Strip from each roll on a shade card in a light box; rolls grouped and labelled by shade group; a wash blanket used where the buyer supplies the recipe | Rolls in the same group visibly different; shade groups not on tickets |
| Shade within a roll | Side-centre-side and start-to-end swatches compared | Edges or one end lighter (tailing, listing) |
| Weight | Circular cutter swatches weighed and converted to ounces per square yard | Outside the stated weight tolerance |
| Skew | Twill and weft lines measured against the selvedge, as a percentage of width, against the mill's target | Skew off target, which shows as leg twist after washing |
| Width | Cuttable width measured along the roll | Narrower than the marker plan needs |
| Fabric faults | 4-point grading on the frame | Points per 100 square yards above the limit |
| Selvedge denim | Selvedge colour line and edge quality along the length | Broken or wavy selvedge where it will show as an outseam |
| Lab samples | Swatches sealed for shrinkage after washing, stretch and recovery (stretch denim) and crocking | Results outside the specification |
A quick on-site wash of a swatch can give an early read on shrinkage and wash-down shade, but the formal results come from an accredited lab.
Common defects in denim fabric
| Defect | What it looks like | Class |
|---|---|---|
| Shade groups mixed in shipment | Panels from one roll set do not match in the garment | Critical |
| Wrong weight or construction | Fabric lighter or heavier than ordered | Critical |
| Rope-dye streaks | Darker or lighter warp-way lines, often clearer after washing | Major |
| Excess skew | Side seams that rotate to the front after washing | Major |
| Weft bars | Bands across the width from a different weft lot or loom stop | Major |
| Elastane faults | Puckering, bubbles or slack places from broken or uneven elastane | Major |
| Slubs outside the intended pattern | Thick places in a non-slub fabric, or clusters in a slub fabric | Minor or major by size |
| Coating or finish marks | Patchy sheen or stiff spots | Minor |
Slub denim is meant to look irregular. Agree a reference roll so the inspector can tell designed slubs from defects.
Rules and specifications
Denim fabric is traded on the mill's specification sheet and the buyer's standards, so most requirements are contractual. Indigo and sulphur dyeing, coatings and the chemicals used later in garment washing are watched closely by brands. REACH restrictions on azo dyes and other substances apply when the fabric is made into clothing for the EU; see azo dyes and restricted substances and REACH. The garment will need a fibre content label, so the elastane and any recycled fibre content declared by the mill should match what is in the roll; see EU textile labelling. Recycled or organic cotton claims need a valid transaction certificate.
Packing, transit and your purchase order
Denim is heavy, and rolls are long. Rolls should be on strong tubes, wrapped in polythene and laid flat, not stood on end, so the fabric does not crease. Indigo rubs off onto light wrapping and onto other goods, so denim should not be packed against light fabrics. The inspector checks that each roll ticket shows shade group, length, width and weight, and that rolls of one shade group are kept together in the container.
Put these in your purchase order:
- Article or quality number, weave, weight in ounces per square yard, width, and fibre content.
- Shade standard and the number of shade groups you accept per lot.
- Skew target and tolerance, residual shrinkage limits in warp and weft.
- For stretch denim: stretch, recovery and growth limits with the test method.
- Crocking grades, dry and wet.
- Fault limit in points per 100 square yards, and how slubs are judged.
- Roll length, ticket content and packing.
For more on how shade and print are judged in dyed goods, see finished and printed fabric. Book an inspection in Ahmedabad or anywhere in India.