What is a nep?#
A nep is a small knot of tangled fibers in the yarn. Most neps come from cotton and are formed during ginning and spinning, especially from immature fibers that are thin and flexible and tangle easily. Some neps include tiny seed coat fragments.
Neps are hard to see in greige fabric but become obvious after dyeing, because immature fibers take up less dye. They show as small white or light specks on a colored background, most visible on dark shades.
What it looks like#
- Tiny white or pale specks scattered over dyed fabric.
- Small raised dots on the surface.
- Specks that are much more visible in navy, black and other dark shades.
- Occasionally, dark specks from seed coat fragments.
Where it occurs#
- Cotton and cotton-rich fabrics, knits and wovens.
- Carded yarns more than combed yarns.
- Dark reactive dyed shades where contrast is high.
Likely causes#
Neps come from the fiber (maturity, contamination) and from the way it is processed (ginning, opening, carding). Dyeing does not create neps but reveals them. Some dyes and dyeing methods cover immature fibers better than others.
Machine-related causes#
- Carding: worn card wires or wrong settings fail to separate fiber tufts, or create new neps.
- Excessive beating and opening that tangles fibers.
Material-related causes#
- Immature cotton: fibers with thin walls tangle easily and dye lighter.
- Seed coat fragments from ginning.
- Low-grade cotton in the mix.
Operator and process-related causes#
- Bale mixing: adding cotton with poor maturity to reduce cost.
- Process settings changed without testing.
Method-related causes#
- Yarn type: carded yarn for products where combed yarn is needed.
- Dyeing: some dye selections and processes cover immature fibers poorly.
- Mercerisation, where suitable, improves dye uptake of immature fibers, but adds cost.
How to confirm the cause#
- Look at specks under magnification: white fiber knots are neps; dark flecks are often seed coat fragments.
- Compare yarn lots and suppliers.
- Check yarn test reports for nep counts, where available.
- Dye test pieces from different yarns with the same recipe.
- Try alternative dye recipes on the same fabric to see if coverage improves.
Immediate containment#
- Inspect dyed rolls under the buyer's light, comparing with an approved standard.
- Separate rolls with visible neps for review.
- For dark garments, avoid cutting heavily affected rolls for visible parts.
Corrective action#
| Cause | Corrective action |
|---|---|
| Immature cotton | Change cotton mix or yarn supplier |
| Carding | Card maintenance and settings at the spinner |
| Carded yarn | Specify combed yarn for dark or premium products |
| Dye coverage | Review dye selection and process with the dyehouse |
Preventive action#
- Yarn specifications with nep or imperfection limits for dark shade programs.
- Test dyeing new yarn lots in dark shades before bulk.
- Supplier approval for yarn used in dark colors.
- Approved standard for acceptable nep level agreed with the buyer.
Inspection notes#
- Inspect dyed fabric at the buyer's viewing distance and light.
- Neps are usually assessed against an approved sample rather than by counting.
- Heavy neps on a garment front can be treated as a defect; light scattered neps may be acceptable. Follow the buyer's standard.
Neps compared with similar faults#
| Fault | How to tell it apart |
|---|---|
| Nep | Tiny fiber knot, usually lighter than the ground after dyeing |
| Slub | Longer thick place along the yarn |
| Seed coat fragment | Dark fleck, sometimes with fibers attached |
| Pill | Formed later by wear or testing, sits on the surface. See pilling |
| Foreign fiber | Different color or luster; often polypropylene or colored fiber from contamination |
Getting the name right matters because each fault goes back to a different supplier or process.
Example investigation#
A black cotton jersey order shows scattered white specks, while the same fabric in grey looks clean. The yarn is carded. Test dyeing the same fabric with an alternative black recipe reduces the visibility of specks but does not remove them. The next lots were switched to combed yarn for black and navy shades, and nep limits were added to the yarn specification.
Factory checklist#
- Yarn type (carded or combed) suited to shade and product
- Nep limits in yarn specification for dark shades
- Test dyeing done on new yarn lots
- Dyed rolls inspected against an approved standard
- Supplier informed of repeated problems
Related guides: slub, shade variation.