Bursting strength is the force or pressure needed to rupture a fabric when it is pushed out in all directions at once, like the knee of a pair of leggings or the elbow of a sweatshirt. It is the standard strength test for knitted fabrics.
Why knits use burst tests#
A tensile test pulls a strip of fabric in one direction. Knits stretch so much in one direction and narrow in the other that a strip test gives results that are hard to interpret. A burst test loads the fabric in all directions together, which is closer to how knitted garments are stressed in wear.
Test methods#
| Method | Principle | Result unit |
|---|---|---|
| ISO 13938-1 | Hydraulic diaphragm: liquid pressure expands a rubber diaphragm under the clamped fabric | kPa (bursting pressure), and bursting distension in mm |
| ISO 13938-2 | Pneumatic diaphragm: air pressure instead of liquid | kPa |
| ASTM D3786 | Hydraulic diaphragm | kPa or psi |
| ASTM D6797 | Constant rate of extension ball burst: a polished steel ball is pushed through the clamped fabric | N or lbf |
Results from diaphragm and ball methods are not directly comparable, and different test areas give different results. Use the buyer's method.
How the diaphragm test works (principle)#
- The fabric is clamped over a circular opening on top of a rubber diaphragm.
- Pressure increases at a controlled rate, bulging the diaphragm and fabric.
- The pressure at which the fabric bursts is recorded.
- The pressure needed to inflate the diaphragm alone (without fabric) to the same distension is subtracted to give the fabric's bursting strength.
- Several specimens are tested and the average is reported.
What affects bursting strength#
| Factor | Effect |
|---|---|
| Yarn strength and count | Stronger, coarser yarns raise burst strength |
| Fabric weight (GSM) | Heavier fabrics usually burst at higher pressure |
| Stitch length | Tighter fabrics (shorter stitch length) often burst at higher pressure |
| Fiber | Synthetic blends usually give higher strength than 100% cotton of the same weight |
| Wet processing | Harsh bleaching, enzyme or chemical treatments can weaken fabric |
| Elastane | Increases distension; effect on burst pressure depends on the fabric |
When results are low#
- Check yarn strength and count against the specification.
- Review bleaching and dyeing conditions for fiber damage (for example, excessive peroxide or enzyme treatment).
- Check whether a lighter GSM or longer stitch length was used than specified.
- Compare with a reference fabric that passed.
Linked garment problems#
Weak fabrics show up as holes at stress points and around seams in wear. See holes. Seam failures are a separate issue; see seam strength.
For woven fabric strength, see tensile strength.
Related guides#
- ISO, ASTM and AATCC test methods: bursting methods by standard.
- Knit vs woven fabric: why knits use burst tests and wovens use tensile tests.
- Fabric testing standards and methods: strength tests within the full test program.
- Different types of knit fabrics: the knit fabrics bursting strength is measured on.
Frequently asked questions#
Can I compare kPa results from different labs? Only if both used the same method, test area and conditions. Ask for the method and test area on every report.
Should garments or fabric be tested? Fabric tests are the norm for material approval. Some buyers also test garment panels, especially from high-stress areas.
Does washing change bursting strength? It can. Some buyers require testing after a set number of washes to check durability.