Two ratings, two questions
Corrugated strength gets reported two ways, and they answer different questions. Mullen (or burst) asks: how much pressure can the board take before it ruptures? ECT — edge crush test — asks: how much weight can the box carry stacked on its edges before it crushes?
Confusing the two leads to over-buying or, worse, under-specifying. The right rating depends entirely on how your box lives its life.
What Mullen tells you
Mullen measures puncture and burst resistance — the board’s ability to resist being poked through or split. It was the traditional standard for decades and still matters where boxes take rough, individual handling and impacts.
If your parcels get thrown, dropped and jostled one at a time through a parcel network, burst strength speaks to how well they survive abuse.
What ECT tells you
ECT measures stacking strength — how much load a box can bear pressing down on it. That is the dominant force in the world of pallets, warehouses and bulk bins, where boxes are stacked high and hold each other’s weight.
For anything palletized, ECT predicts real-world performance far better than burst does. A high-ECT box holds a tall stack; a high-Mullen box merely resists being punctured.
“Stack boxes on a pallet and ECT is the only number that matters.”
Choosing between them
ECT has also become the more common modern spec because it correlates better with stacking and uses less fiber for the same performance, which is both cheaper and greener.
- Palletized, stacked, warehoused loads → specify by ECT.
- Single-parcel, rough-handled, high-impact loads → burst strength is relevant.
- Bulk bins and Gaylords → ECT and wall count, essentially always.
- Regulated or carrier-mandated loads → use whichever the rule cites.
The practical takeaway
For the bulk and palletized world we mostly live in, think in ECT and wall count. When a customer needs certified numbers for a compliance or export load, we can supply ECT and Mullen certificates on the appropriate stock.
Tell us how the load ships and stacks, and we will point you at the rating that actually governs whether your box holds up.