Our heather grey tees show faint horizontal stripes across the body. What causes it?
Faint repeating bands across knit fabric are usually barré, caused by differences between yarn ends, lots or knitting tension. It is best prevented at the mill.
A bulk order of heather grey tees has faint horizontal stripes on many pieces, visible mostly in daylight. The sample fabric didn't have them. The factory says heather always varies a bit. Is that true?
Main answer
Faint horizontal bands that repeat across knit fabric are usually called barré. On a circular knitting machine, many yarn ends feed the machine at once, and each knits its own course around the tube. If some of those yarns differ, even slightly, in thickness, twist, fibre blend or dye uptake, the courses they knit look different and form a band pattern. Heather and melange yarns are a blend of fibres in different shades, so small differences in the blend between yarn lots show up easily. Variation in heather is normal; visible regular stripes are not.
Common causes
Mixing yarn from different lots or spinners on one machine is a frequent cause. Uneven yarn tension at the feeders can change stitch length on some courses. Differences in yarn twist or count can also show. For dyed fabrics, the yarn's dye uptake can differ between lots, but heather greys are often made from pre-dyed fibres, so blend ratio is the usual suspect.
How to check
Look at the fabric in daylight and at an angle, from a few metres away; barré is often easier to see from a distance. Measure the distance between bands. A repeat that matches the number of feeders on the machine points to a feeder or yarn issue. Ask the mill for the yarn lot records and knitting machine for the affected rolls.
What to put in the spec
Require single-lot yarn per order or per colour where possible, and ask the mill to segregate lots and not mix them on a machine. Give a fabric weight tolerance with a named method such as ASTM D3776, since stitch length changes affect weight. State that visible barré under agreed viewing conditions is a defect, and ask the mill to inspect rolls for it before shipping fabric to the cutting room.
Bulk already made
If the problem affects only some rolls, cutting can sometimes be planned so pieces from different rolls are not mixed in one garment. Washing does not usually remove barré; check by washing a piece with a named procedure such as ISO 6330. Inspect finished garments as a sample under ISO 2859-1 with barré listed as a major defect.
Sources and further reading
- ASTM D3776/D3776M — Mass per Unit Area (Weight) of Fabric
- ISO 6330:2021 — Domestic washing and drying procedures for textile testing
- ISO 2859-1 — Sampling by attributes indexed by AQL (1999 edition page, showing its 2026 revision)
Standards and rules are summarised from their published scope or official guidance. Use the current edition and confirm requirements for your market.
Three perspectives on this question
Purchasing perspective
I'd write single-lot yarn and roll inspection into the fabric purchase order, and ask the mill to tell us before any yarn change.
Merchandising perspective
Heather grey is a core colour for basics. A striped batch looks like a quality failure, so I'd rather hold it than sell it.
QC perspective
We'd inspect a sample of garments in daylight at arm's length and from a distance, and compare with a bulk-approved fabric header.
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