When a bag is overstuffed until the panels bulge, the fabric usually fails by bursting — a single hole opening around a stress point — rather than by tearing along a seam. Bursting strength measures the pressure a woven cloth takes before it ruptures, and for overstuffed duffels, tool bags and golf travel cases it is a more honest specification than tear strength. Put a minimum burst pressure (kPa or psi) in your purchase order and you get a measurable, repeatable incoming-quality check instead of a fist-test at the factory gate.
What bursting strength actually measures
In a Mullen (diaphragm) burst test, a circular fabric sample is clamped flat between two rings. A rubber diaphragm is then pushed up against the cloth with rising pneumatic pressure until the material ruptures. The peak pressure at rupture is the bursting strength.
The method captures the whole cloth structure at once — warp and weft threads together, plus the coating or laminate that holds them. That is different from a grab tensile test, which only pulls the fabric in one direction. Most buyers reference ISO 13938-1 for textiles and ASTM D3786 for knitted or coated cloth. Results are reported in kilopascals (kPa), pounds per square inch (psi) or kgf/cm².
Burst vs tensile vs tear — which to specify
These three numbers answer different questions, and mixing them up is the most common spec mistake:
- Tensile (grab) strength — how much one-direction pull the fabric survives.
- Tear strength — how easily a slit propagates once it has started.
- Bursting strength — how the fabric resists omnidirectional pressure from the inside.
An overstuffed bag pushes outward in every direction at once, so burst strength is the better predictor of real-world failure. We still recommend pairing it with the fabric tensile and tear strength profile so you understand both the panel and the seam behavior.
Typical numbers by fabric
Exact values are set by the buyer in the purchase order — there is no single “industry standard” number you must copy. As a planning guide, common ranges look roughly like this:
- 210D lightweight nylon: ~150–300 kPa
- 500D–1000D coated nylon / PU: ~250–600 kPa
- 12–18 oz canvas (cotton or poly-cotton): ~400–900 kPa
- rPET 600D: similar to nylon of the same denier
Coatings and films raise burst pressure because they bridge the weave; a TPU-laminated panel will test higher than the same base cloth uncoated. The denier and coating choice therefore drives the number more than most buyers expect, which is why the fabric spec and the burst spec belong in the same tech pack line.
Writing a burst spec into your tech pack
A usable burst requirement has four parts:
- Minimum pressure per fabric (e.g., “600D body fabric: no sample below 350 kPa”).
- Test standard — ISO 13938-1, with sample diameter stated.
- Sampling — how many cuts per production lot.
- Acceptance — lot pass/fail tied to an AQL inspection plan so the factory knows exactly when a roll is rejected.
This turns a vague “make it strong” into something the QA line can actually run. Abrasion resistance also affects how long that burst number holds up in use, so pair the two checks for outdoor and sports lines.
When burst strength matters most
Burst specs earn their keep on bags that get crammed: overstuffed duffels, tool bags, golf travel cases and dive bags. A low minimum lets a cheaper, weaker cloth through, and the symptom shows up later as returned “exploded” bags rather than at incoming inspection. Setting the floor is cheaper than dealing with the returns.
Frequently Asked Questions
What unit is fabric bursting strength measured in?
Kilopascals (kPa) under ISO 13938-1, though many factories also quote psi or kgf/cm². Always state the unit in the PO so the number cannot be reinterpreted.
Is burst strength the same as tear strength?
No. Tear strength measures a slit propagating in one direction; burst strength measures resistance to pressure from all directions at once. An overstuffed bag fails by bursting, so burst is usually the more relevant spec.
What burst pressure should I specify for a duffel bag?
It depends on the denier and how the bag is used, but a 500D or heavier duffel body is often specced at 300 kPa and up. The buyer sets the value in the PO rather than copying a fixed figure.
How do I test fabric burst at the factory?
Use a Mullen diaphragm burst tester per ISO 13938-1, cut samples from each production lot, and apply an AQL-based acceptance rule so the lot passes or fails on a defined sample, not on a single lucky cut.
Conclusion
Bursting strength is the specification that matches how bags actually fail — by bulging and rupturing, not by tearing neatly. Write a minimum pressure into the tech pack, tie it to ISO 13938-1 and an AQL lot check, and you get a fabric gate that protects the whole order. For the wider set of checks that belong in a factory QA plan, see our guide to bag quality control checkpoints.