Burst strength (Mullen)
Burst strength is the pressure required to rupture a paper or board sample, applied through a rubber diaphragm by a Mullen tester. It is reported in psi or kPa and is one of the oldest standardised paper strength tests.
The Mullen tester clamps a circular sample over a flexible rubber diaphragm; hydraulic pressure inflates the diaphragm until the paper bursts. The pressure at burst is the result. Simple, repeatable, and historically the standard for box-grade certification.
Burst was the basis of the U.S. Carrier Classification (Rule 41) box-strength requirements for decades. For boxes intended to stack on pallets, edge crush test (ECT) has largely displaced it because ECT better predicts stacking strength. Burst is still common on bag papers, kraft papers, and as a quality-control checkpoint at mills.
Typical values: a 42-lb kraft linerboard runs around 90 psi burst; heavy multi-wall sack kraft can exceed 200 psi.
Related terms
- Edge crush test (ECT)ECT measures the edgewise compressive strength of a corrugated board, reported in pounds per inch or kN/m. It is the standard predictor of stacking strength and has largely replaced burst strength as the spec for box certification.
- Tensile strength (paper)Tensile strength is the maximum stretching force a paper or board can withstand before breaking, measured in machine direction and cross direction. It is reported as kN/m or as breaking length in metres.
- LinerboardLinerboard is the flat, smooth paper layer bonded to either side of a corrugated medium to form a corrugated board. It provides the strength, printability, and outer surface of a cardboard box.
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