Finishing
What happens to fabric between the knitting machine and the cutting table, and what each finish gives the buyer. By the end you will know which shrinkage and spirality limits to write into a specification.
Preparation before dyeing
Fabric straight from the machine, greige fabric, carries cotton’s waxes and pectins, knitting oils and, if woven, size. It wets slowly and dyes unevenly. Preparation, usually in the order below, makes it clean, absorbent and, where needed, white.
- SingeingFlames or hot plates burn off protruding fibres: a cleaner surface and less pilling. Mainly for wovens, and for yarn (gassed yarn).
- DesizingEnzymes or oxidisers remove the size put on warp yarn for weaving; knitted fabric has none.
- ScouringHot alkali removes waxes, pectins and oils so that the fabric wets out quickly and evenly.
- BleachingHydrogen peroxide removes cotton’s yellowish tint: fully for whites and pale shades, partly before dark ones.
- MercerisingStrong caustic soda under tension changes the cotton fibre for good: more lustre, strength and dye uptake, so deep shades need less dye.
Mechanical and chemical finishes
After dyeing, finishes set the hand, look and performance. Mechanical finishes change the structure or surface; chemical ones add a substance that coats or bonds to the fibre.
| Finish | Type | What it does | What the buyer gets |
|---|---|---|---|
| Compacting | Mechanical | Steam and overfeed push the knitted loops together lengthwise | Lower length shrinkage; GSM rises slightly |
| Sanforising | Mechanical | A rubber belt on a heated drum compresses woven fabric lengthwise | Wovens that keep their length in washing |
| Calendering | Mechanical | Heated rollers press the fabric | A smooth, sometimes lustrous surface; may fade in washing |
| Raising (brushing) | Mechanical | Wire rollers pull fibre ends into a soft pile | A warm fleece back; more fibre to pill |
| Peaching | Mechanical | Abrasive rollers raise a very short nap | A soft, suede-like touch |
| Shearing | Mechanical | Blades cut the pile to an even height | An even pile on velour, terry and fleece |
| Softening | Chemical | Cationic, polyethylene or silicone softeners coat the fibre | A softer hand, easier sewing; excess silicone cuts absorbency and can undo compacting |
| Bio-polishing | Chemical (enzyme) | Cellulase removes protruding microfibres | A cleaner surface, clearer colour, less pilling; slight loss of weight and strength |
| Anti-pilling | Chemical | Bio-polishing on cotton; polymer finishes on blends | Fewer pills |
| Water-repellent | Chemical | Lowers the fibre’s surface energy so water beads | Sheds light rain; PFAS-free chemistry is now widely required |
| Easy-care | Chemical | Resin crosslinks the cellulose | Less creasing and shrinkage; lower strength and abrasion resistance |
Resins are the main source of formaldehyde in cotton fabric: OEKO-TEX STANDARD 100 allows 75 mg/kg next to the skin and none detectable in babies’ articles. Specify each finish together with the test that proves it.
Shrinkage and spirality
Cotton swells when wet. Knitting, dyeing and drying stretch the loops lengthwise; washing and tumble drying let them return to a rounder, relaxed shape, and the fabric shrinks. Finishing removes most of this before cutting: low-tension drying relaxes the fabric and compacting pushes the loops to their relaxed length. What remains, residual shrinkage, is what the buyer’s test measures. Its consistency matters as much as its value: the pattern maker builds it into the pattern, so rolls that vary make garments that vary.
Spirality is the slant of the wales in single jersey after washing, seen as a side seam twisting to the front. It comes mainly from single-yarn torque and the many feeds of a circular machine. Finishing can straighten and stabilise fabric but not remove torque; twist, plied yarn and the knitting set-up control that.
- ±5%a common limit on the length and width change of cotton knits after washing and tumble drying
- ±3%a common limit for cotton woven fabric
- 5%a common maximum spirality for single jersey after washing
Tubular or open-width
A circular machine knits a tube. The finisher keeps it tubular or slits it along a marked wale line and finishes it flat.
| Point | Tubular | Open-width |
|---|---|---|
| Handling | Dyed, dried and compacted as a tube | Slit, dried and set to width on a stenter, compacted flat |
| Width | Set mainly by machine diameter and gauge | Set on the stenter to the width ordered |
| Typical use | Basic T-shirts, underwear, body-size tubes without side seams | Elastane fabric (needs heat setting), print bases, large markers |
| Watch for | Fold lines along both edges | Pin holes reduce usable width; a slit off the wale line causes skew |
Terms in this chapter
See it in our production
Sources
- Cotton Incorporated ISP 1009: Guide to Improved Shrinkage Performance of Cotton Fabrics (opens in a new tab)cottoninc.com
- Cotton Incorporated TRI 3011: Wet Processing of 100% Cotton Knitted Fabrics (compaction, resin finishing, slitting, tenter) (opens in a new tab)cottoninc.com
- Cotton Incorporated TRI 2002: Knit Fabrics and the Reduction of Torque (opens in a new tab)cottoninc.com
- ISO 5077: Textiles — Determination of dimensional change in washing and drying (opens in a new tab)iso.org
- OEKO-TEX STANDARD 100, Annex 4: product-class-specific limit values (formaldehyde, pH, colour fastness) (opens in a new tab)oeko-tex.com
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