A garment is only as strong as its seams. Seam tests check whether seams will hold in wear, and whether the fabric pulls apart at the seam line before the thread breaks.
Two different tests#
| Test | What it measures | Typical fabrics |
|---|---|---|
| Seam strength | Maximum force needed to rupture a sewn seam | Wovens, especially bottoms, workwear, outerwear |
| Seam slippage | Force at which a set seam opening occurs, or the opening at a set force | Loose or slippery wovens: satins, chiffons, viscose, polyester filament fabrics |
Methods#
- ISO 13935-1 (strip method) and ISO 13935-2 (grab method): seam tensile properties, maximum force to seam rupture.
- ISO 13936-1 (fixed seam opening) and ISO 13936-2 (fixed load): resistance to slippage of yarns at a seam in woven fabrics.
- ASTM D1683: failure in sewn seams of woven fabrics.
Test specimens can be taken from garments or prepared with a standard seam. Buyers specify the method, the specimen type and the minimum requirements.
How seams fail#
| Failure mode | What happens | Likely fix |
|---|---|---|
| Thread breaks | Stitches break before the fabric | Stronger thread, higher SPI, different stitch type |
| Fabric breaks at stitch line | Needle holes weaken the fabric | Finer needle, lower SPI, ball point for knits |
| Seam slippage | Yarns slide out of the seam, leaving an opening | Wider seam allowance, different seam type, fabric with better slippage resistance, higher SPI |
| Fabric tears away from seam | Fabric too weak near the seam | Check fabric strength and finishing |
Ideally, a seam should be slightly weaker than the fabric, so that a failure can be repaired rather than tearing the fabric.
What affects seam performance#
- Thread: type, strength and ticket. See sewing thread selection.
- Stitch type: lockstitch, chainstitch, safety stitch and overlock behave differently. See stitch types.
- Stitch density: more stitches per inch generally increase strength, until needle damage weakens the fabric. See stitch density.
- Seam type and allowance: felled and bound seams are stronger than plain seams; wider allowances resist slippage.
- Fabric: construction, yarn friction and finishing (softeners can increase slippage).
Seam slippage in practice#
Slippage shows on garments as seams that open up with a line of visible yarns, especially at stress points such as back seams on dresses, armholes and trousers. Causes include loose fabric construction, smooth filament yarns, silicone softeners and narrow seam allowances.
Practical checks in the factory#
- Pull tests on sample seams by hand during production (not a replacement for lab tests, but useful for early warning).
- Check SPI and seam allowance against the specification on the line.
- Test the first bulk garments, not only fabric samples.
Linked defects: open seam, seam grin and broken stitch.
Related guides#
- Tensile strength: fabric strength, which the seam should not exceed.
- Fabric testing standards and methods: seam tests within the full test program.
- Sewing needle selection: needle damage that weakens fabric at the seam.
Frequently asked questions#
Which seams should be tested? Usually the seams under the most stress in wear: crotch and back rise on trousers, side seams and armholes on fitted garments, and main seams on workwear. The buyer's test program may name them.
Does a pass on fabric samples guarantee garments pass? No. Test seams from bulk garments made on production machines, because thread tension, SPI and seam allowance on the line can differ from the lab sample.
Is seam slippage a problem for knits? Much less so. Slippage tests are designed for woven fabrics where yarns can slide.