What Is Bursting Strength and Why Does It Matter?
An explanation of bursting strength, how it is measured, what bursting factor means against GSM, and when it is the wrong metric to rely on.
Bursting strength is one of the oldest and most widely quoted measures of corrugated board quality in India, and also one of the most misunderstood. It tells you how much pressure a piece of board can withstand before it ruptures — a useful figure, but only for certain kinds of failure.
How it is measured
Bursting strength is tested using the Mullen test, where a rubber diaphragm is pressed against a flat sample of board until it ruptures. The pressure at rupture is recorded in kilograms-force per square centimetre (kgf/cm²). This has been the standard test for corrugated and paperboard for well over a century because the equipment is simple and the test is quick to run on the factory floor.
Bursting factor versus GSM
Bursting factor (BF) expresses bursting strength relative to the weight of the paper, so that papers of different GSM can be compared fairly. A higher BF at the same GSM means a stronger, better-quality paper for a given weight — which is why two boxes made from paper of identical GSM can still have noticeably different strength if their BF differs.
When bursting strength is the right metric
BF is most relevant when a box faces puncture risk, rough manual handling, or impact from sharp corners and edges — conditions common in road transport with multiple loading and unloading points, or where cartons are handled by hand rather than moved on pallets. It answers the question: will this box tear or puncture under abuse?
When edge crush matters more
Bursting strength does not predict how well a box will hold up under sustained stacking weight — that is the job of the edge crush test (ECT), which measures the flute's resistance to being crushed edgewise. For boxes that spend most of their life stacked in a warehouse or on a pallet rather than being handled roughly, ECT is usually the more predictive figure, and relying on BF alone can leave you with a box that survives handling but collapses under its own stack.
A high bursting strength figure tells you a box resists puncture. It does not tell you whether the same box will still be standing after three weeks at the bottom of a pallet stack.
When specifying a box, ask for both BF and ECT figures rather than one in isolation, and match the emphasis to how the box will actually be handled and stored.
Not sure which strength metric your box needs?
Tell us how your product is packed, stacked and transported and we will recommend the right BF and ECT combination.
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