What is an open seam?#
An open seam is a seam where the two pieces of fabric are not held together along part of its length. The stitches either did not catch one of the fabric edges, or they were formed but later broke or unravelled. Either way, there is a gap in the garment where there should be a closed seam.
Open seams are one of the most frequent defects found at end-of-line checking, and most buyer manuals treat an open seam on a main seam as a major defect.
What it looks like#
- A visible gap between panels along a seam, sometimes small enough to find only by stretching.
- Stitches running beside the fabric edge instead of through it.
- On overlock seams, the fabric edge of one ply outside the stitch.
- A seam that opens gradually in wear or washing because the edge was barely caught.
Where it occurs#
- Side seams, shoulder seams and sleeve attach on knit garments, especially at curves.
- Crotch and inseam joins where several seams cross.
- Collar, cuff and pocket attach where edges must be aligned by hand.
- Seam ends, where the operator starts or finishes without securing the stitch.
Likely causes#
Most open seams come from one of two things: the fabric edge was not inside the stitch (alignment, allowance, knife setting), or the stitches failed after sewing (broken, skipped or unravelled stitches). Looking closely at the defect usually tells you which: if the stitches are intact but beside the edge, it is an alignment or allowance problem; if the stitches are broken or missing, it is a stitch formation problem.
Machine-related causes#
- Overlock knife cutting too much. The knife should trim just enough to leave the specified seam width. A knife set too far in reduces the fabric caught in the stitch, especially on curves.
- Guides and folders. A missing or badly set edge guide lets the fabric wander.
- Stitch failure. Skipped stitches on chainstitch and overlock seams can unravel and open the seam. See skipped stitch.
- Feed problems. Worn feed dogs or wrong differential feed make one ply move faster, so the edges drift apart along the seam.
Material-related causes#
- Fraying or slippery fabrics lose yarns from the edge, so a narrow seam pulls out.
- Cutting inaccuracy. Panels cut smaller than the pattern, or with wavy edges from a leaning blade, leave less fabric in the seam.
- Loose weaves and some viscose or filament fabrics can slip out of the seam under stress. See seam grin.
Operator and process-related causes#
- Misalignment when loading the panels, especially at the start of the seam.
- Pulling one ply, which makes the edges separate towards the end of the seam.
- Speed at curves, where the operator cannot keep the edges together.
- New or rotated operators who are not yet used to the operation.
Method-related causes#
- Seam allowance too narrow in the pattern for the fabric and stitch.
- No secure seam ends: chainstitch and overlock seams need the chain secured or crossed by another seam.
- Operation sequence that leaves edges unsupported, for example sewing a curved seam without notches.
How to confirm the cause#
- Look at the defect under good light. Are the stitches intact beside the edge, or broken or missing?
- Measure the seam width on several pieces from the same operator and machine. Compare with the specification.
- Check cut panel sizes against the pattern, especially at the area where the seam opens.
- Watch the operation for alignment and pulling.
- Sort the defects by operator and machine using end-of-line records. If they come from one machine, check its settings first.
Immediate containment#
- Stop the operation and check the current bundle and the previous bundles from the same machine.
- Pull-test the seam on sewn garments: open seams that are nearly caught will show.
- Repair affected garments by resewing the seam over the full affected length, with overlap onto the good seam.
- Inform end-of-line and finishing checkers to check this seam on every garment until the cause is fixed.
Corrective action#
| Cause | Corrective action |
|---|---|
| Knife cutting too much | Reset knife position to leave the specified seam width |
| Guide missing or wrong | Fit and set an edge guide |
| Stitch failure | Fix skipped or broken stitches: needle, timing, tension |
| Feed imbalance | Adjust differential feed; replace worn feed dogs |
| Undersize panels | Check cutting accuracy, blade condition and marker |
| Operator alignment | Retrain on loading and guiding; supervise the first pieces |
| Allowance too narrow | Increase allowance in the pattern for the style |
Preventive action#
- Include seam width checks in machine setup for each style.
- Record knife and guide settings by style and fabric.
- Add seam pull tests to inline inspection on critical seams.
- Check cut panel accuracy at cutting with top and bottom ply checks.
- Review seam allowances at pattern approval for fraying and slippery fabrics.
Inspection notes#
- Check seams by stretching them gently along and across, not just visually.
- Pay attention to seam starts, ends and crossings.
- On overlock seams, look at both plies' edges inside the stitch.
- Record the operation that caused the defect so it can be traced. See DHU.
Factory checklist#
- Seam width measured against specification
- Overlock knife and edge guide set for the style
- Differential feed adjusted for the fabric
- Cut panels checked for size and edge quality
- Operators trained on alignment at curves and seam starts
- Seam ends secured
- Seam pull tests in inline inspection
Related guides: broken stitch, skipped stitch, seam strength testing.