Illustrative situation
A brand finds that some T-shirts have gaps in hem stitching and a few seams pop when the shirt is pulled on. The factory blames the fabric. The buyer wants to know what to check and how to specify it.
Main answer
Skipped stitches and burst seams come from a wrong or worn needle, unsuitable thread, poor tension, a stitch type that cannot stretch with the knit, or sewing with the fabric under strain. Specify the stitch type and thread for each seam, and test how the seam behaves when stretched before approving bulk.
Skipped stitches
A skipped stitch is a point where the needle did not catch the loop of thread. In knits, causes include a blunt or wrong needle type, fabric that flags or moves, incorrect timing or tension on the machine, and elastic fibres that spring back. They appear as gaps in a seam and weaken it, especially at the hem and at stress points.
Broken or burst seams
Seams burst when the stitches cannot extend as far as the fabric does. A lockstitch seam in a stretch knit has little give and can break when the garment is pulled on. Thread that is too weak or too thick, stitches that are too long or too short, and seam allowance that is too narrow also contribute. Heat and repeated washing can weaken some threads.
Choosing the stitch type
ISO 4915 classifies stitch types into classes, such as lockstitch, multi-thread chain stitch, overedge and covering stitches, with numeric codes. For knits, stitch classes that stretch, such as overedge and covering stitches, are often used on hems and seams that need to extend. Ask the factory to name the stitch type for each seam rather than just saying "stretch stitch".
How to test it
Pull the seam gently in the direction it stretches in wear and check that stitches extend with the fabric and recover without gaps. AATCC TM88B addresses the smoothness of seams after home laundering, which shows that seams are evaluated after washing, and seam appearance can reveal tension problems. Wash and re-check. Inspect hems under light for skipped stitches. See product options on pajamas and T-shirts.
Fact, recommendation, uncertainty
- Established fact
- ISO 4915 classifies stitch types into defined classes with numeric codes, which gives buyers and factories a common vocabulary.
- Recommendation
- Name the stitch type and thread for each seam, test stretch and recovery of seams and check hems for skipped stitches.
- Uncertainty
- We found no single seam-strength number for all knitwear, so targets should be set per product and use.
Sources and further reading
- ISO 4915:1991 — Textiles: stitch types, classification and terminology
- AATCC TM88B — Smoothness of Seams in Fabrics after Home Laundering
Sources checked on 24 October 2026. Standards bodies sell the full texts; we cite what their public pages state. General information, not legal or technical certification advice.
More perspectives from the team
Three further views on the same question, each by function. They add conditions and limits to the main answer; they are editorial notes, not customer reviews.
Sino Finetex Editorial Team Sourcing
Ask the factory to list stitch types and thread by seam in the quotation. Limit: a general description may hide a cheaper stitch. Ask whether needles are changed on a schedule and how broken needles are tracked.
Sino Finetex Editorial Team Product selection
Choose seam types by function: use stretch stitches where the garment extends, and stronger stitching at stress points. Limit: stronger seams can add bulk or cost. Avoid specifying a fine, dense stitch that is too stiff for a stretchy fabric just because it looks neater.
Sino Finetex Editorial Team Quality & care
Include a seam stretch check and a skipped-stitch check in inline and final inspection. Limit: a visual check misses weak seams, so combine it with a pull test. Check a few garments by gently stretching the hem and side seams in the direction of wear.
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