A garment seam is a small system: two layers of fabric, a sewing thread, a stitch type, a stitch density and the needle holes the machine has punched. When a seam test gives a disappointing figure, any one of those may be responsible — and the force alone does not tell you which.
ISO 13935 measures the maximum force a seam withstands when pulled at right angles to it. Used well, it tells you where the seam is weak. Used carelessly, it gives a number that cannot be compared with anyone else's.
Strip or grab
| ISO 13935-1 | ISO 13935-2 | |
|---|---|---|
| Method | Strip | Grab |
| Specimen held | Across its full width | In the centre only, by narrower jaw faces |
| Machine | Tensile tester (CRE) | Tensile tester (CRE) |
The standard warns that results from one method should not be compared with results from the other. The reasoning is the same as for fabric tensile testing: in a grab test, fabric outside the jaws contributes to the load, so grab figures usually come out higher than strip figures on the same seam.
Both parts apply to woven fabrics, including those with stretch properties, and only to straight seams. ISO 13935-2 is normally not applicable to geotextiles, nonwovens, coated fabrics, glass-fibre wovens, carbon-fibre fabrics or polyolefin tape fabrics. Check the edition as well: a new edition of ISO 13935-2 was published in 2026, and contracts often still reference the earlier one.
The failure mode is part of the result
Every specimen should be inspected after it breaks, and the type of failure recorded. In practice four outcomes occur:
- Fabric breaks away from the seam. The seam is stronger than the fabric. The figure is really a fabric strength.
- Fabric breaks along the stitch line. Needle damage or too high a stitch density has perforated the fabric.
- Sewing thread breaks. The thread or the stitch type is the weak link.
- Seam slippage. Yarns slide out of the fabric at the seam until it opens, without anything breaking.
The same force can arise from any of these, and each calls for a different remedy — a different thread, a different needle, fewer stitches per centimetre, or a different fabric construction. A report that gives only the maximum force throws away the most useful information the test produces.
Seam strength is not seam slippage
Seam slippage — the opening of a seam under a defined load — is a separate property with its own standards, the ISO 13936 series. A fabric with smooth filament yarns may hold a high seam strength while opening visibly at a much lower load. If the complaint from the field is "the seam opens", seam strength is the wrong test.
Who sewed the seam?
Seams tested in a laboratory come from two sources: cut from finished garments, or sewn in the lab from fabric. Both are valid; mixing them without saying so is not.
When the lab sews the seam, every parameter that affects the result should be agreed and recorded:
- seam type and stitch type
- sewing thread (fibre, construction, linear density)
- needle size and point type
- stitch density
- seam allowance
- direction of the seam relative to warp and weft
Change the stitch density alone and the failure mode can shift from thread break to fabric break at the stitch line. Without the recorded parameters, a later retest cannot reproduce the seam.
When seams are cut from garments, note the garment location. Shoulder, side and crotch seams in the same garment can perform very differently.
Set-up details that move the result
Seam position. The seam must lie midway between the jaws and parallel to them. A seam that is off-centre or at an angle is loaded unevenly and fails early on one side.
Jaw slippage. Seamed specimens are thicker and less uniform than plain fabric. If the specimen slips in the jaws, the curve shows it as a saw-tooth or a slow drift. Use jaw faces suitable for the fabric — rubber or grooved — and the correct clamping pressure.
Jaw breaks. A specimen that breaks at the jaw edge has not tested the seam. Record and treat it as the standard requires.
Conditioning. Fabrics and threads both change strength with moisture. Condition specimens to ISO 139.
ISO 13935 and ASTM D1683
North American specifications often call for ASTM D1683 for sewn seams. It is a separate method with its own specimen and procedure. Do not report an ISO 13935 result against an ASTM D1683 limit or the reverse.
Before you report
- Strip (13935-1) or grab (13935-2), and which edition?
- Seam cut from a garment, or sewn in the lab — and are sewing parameters recorded?
- Seam centred and parallel to the jaws?
- Failure mode recorded for every specimen?
- Was the complaint actually about seam opening, which is ISO 13936?
- Specimens conditioned to ISO 139?
Our fabric tensile testers and universal testing machines run both parts of ISO 13935, with interchangeable strip and grab jaw faces. They are built in our own workshop in Istanbul.