When you order a corrugated box, two specifications quietly determine whether your product arrives intact or crushed: Edge Crush Test (ECT) and Bursting Strength (Mullen test). They sound interchangeable, but they measure completely different forces — and picking the wrong one is one of the most common (and most expensive) packaging mistakes.
What Bursting Strength measures
Bursting strength — often called the Mullen test — measures the pressure required to rupture the wall of the board, expressed in kilograms per square centimetre (kg/cm²) or pounds per square inch (psi). A rubber diaphragm pushes against the board until it bursts.
In practice, burst strength tells you how well a box resists puncture and rough handling — being dropped, dragged, or hit by a forklift. It correlates strongly with the basis weight of the paper used.
Rule of thumb: high burst strength = good protection against impact and puncture.
What the Edge Crush Test measures
The Edge Crush Test measures the stacking strength of the board — how much top-to-bottom compression a box can take before the walls buckle. A short piece of board is stood on edge and crushed; the force at failure is the ECT value, expressed in lb/in or kN/m.
This matters because boxes spend most of their life stacked — on pallets, in warehouses, in shipping containers. The box at the bottom of the stack carries everything above it.
Rule of thumb: high ECT = good resistance to stacking and warehouse compression.
So which one do you need?
It depends on how your product is handled:
| Scenario | Prioritise |
|---|---|
| Heavy single items, rough handling, export | Burst strength |
| Lightweight goods stacked high on pallets | ECT |
| Long warehouse storage in humid conditions | ECT (with moisture allowance) |
| Sharp or dense products that can punch through | Burst strength |
Most modern supply chains have shifted toward ECT-based specifications because palletised, stacked distribution is the norm and ECT board uses less fibre for the same stacking performance — making it lighter and more cost-effective.
The humidity factor everyone forgets
Corrugated board can lose up to 50% of its compression strength at high humidity. If your goods travel through monsoon regions or sit in un-conditioned warehouses, build in a safety margin — typically 1.5× to 2× the calculated load — or specify moisture-resistant liners.
How to give us the right brief
You don't need to know the exact ECT or burst number. Tell us:
- The weight of the packed product.
- The maximum stack height in storage and transit.
- The handling environment (manual, forklift, export, humidity).
- How long boxes sit in storage before use.
From there our team back-calculates the required board grade, flute and ply — so you pay for exactly the strength you need, not more.
Want help spec'ing your box? Talk to a packaging specialist and we'll engineer it with you.
