ECT versus burst test
Edge crush test (ECT) rates how much stacking load a box can take; burst, or Mullen, test rates how much pressure it takes to break through the board. For single wall, 32 ECT and 200# test are both rated to 65 lb of box and contents.1
| Grade | Wall | Rated by | Box and contents up to |
|---|---|---|---|
| 32 ECT | Single | Edge crush | 65 lb |
| 200# test | Single | Burst (Mullen) | 65 lb |
| 44 ECT | Single | Edge crush | No figure in our sources |
| 48 ECT | Double | Edge crush | 100 lb |
| 275# test | Double | Burst (Mullen) | 100 lb |
Ratings for 32 ECT, 200#, 48 ECT and 275# from Paper Mart.
What each test measures
The edge crush test stands a short strip of board on its edge and presses down until it crushes. The result, in pounds per inch of edge, predicts how well a box made from that board resists being stacked on. A box sitting at the bottom of a pallet for a month is under exactly that load.2
The burst test clamps a sheet and pushes a rubber diaphragm into it until the board ruptures. The result, in pounds per square inch, is printed as the # test: 200#, 275# and so on. It predicts how the board stands up to puncture and to being thrown about.
Why two systems exist
For many years the burst test was the standard, and the certificate on a box listed burst strength and the combined weight of the liners. Edge crush came in as an alternative because stacking is what most boxes fail at, and because board can reach a given ECT with less paper. Both ratings appear on box maker's certificates today, and a box carries one or the other.3
Which one to ask for
Choose ECT for boxes that ride on pallets and spend time in storage: cases from a food plant, cartons in a warehouse, anything that is stacked. ECT board is usually lighter for the same stacking strength, which can lower the price.
Choose burst-rated board for boxes that travel alone through parcel networks or are handled roughly, where a corner hit or a puncture is more likely than a slow crush. Many e-commerce shippers use 32 ECT for most orders and 200# for heavy or fragile ones.
Over 65 lb of box and contents, neither single wall grade is right. Double wall, at 48 ECT or 275#, is rated to 100 lb.
What humidity does
Corrugated board takes up moisture from the air, and wet board loses much of its strength. Boxes stored in a damp warehouse or a cooler stack less well than the rating suggests. If yours will spend time cold or damp, say so on the quote and allow for it with a stronger grade.
Quick reference
Under 65 lb, stacked: 32 ECT. Under 65 lb, thrown: 200#. Heavy stacking or damp storage: 44 ECT, or double wall. Up to 100 lb: 48 ECT or 275# double wall. Beyond: triple wall, crating, or an engineered pack. Fragile, valuable or unusual items: ask, because the right answer depends on the product as much as the weight, and occasionally foam, molded pulp or suspension packaging serves best.
Recycled fibre and ratings
Boxes made with a high share of recycled fibre can meet the same ECT as virgin board, often with heavier paper to make up for shorter fibres. A rating is a rating whatever the furnish. If you have sustainability targets, ask about recycled content; the certificate stays the measure of strength.
Choosing for your shipment
Picture the box's whole journey. If it leaves a plant on a pallet, sits in a warehouse, travels in a full truck and is unloaded by forklift, stacking dominates: choose ECT. If it is picked, packed alone, sorted by conveyors, thrown into a van and carried up steps, knocks dominate: consider burst. If it does both, at weight, step up to double wall.
Mullen test at a glance
A Mullen tester clamps a sample and inflates a diaphragm beneath it with hydraulic pressure until the board ruptures. The burst figure reflects the toughness of the liners more than the medium. It remains useful for boxes that must survive rough, single-piece handling, and some industries still specify it by habit or contract.
An ECT test cuts a small sample, stands it on edge in a compression tester, and reads the peak load per inch. Both tests follow published standards so that results from different labs can be compared.
Beyond the two numbers
Box compression strength, the load a whole empty box withstands before it buckles, depends on the board's ECT, its thickness and the box's perimeter. That is why a larger box made of the same board can stack better than a small one, up to a point, while wide panels tend to bow. Plants use formulas that combine those factors to choose the board for a target compression.
Real conditions eat into that strength: humidity, time under load, poor stacking patterns, overhang beyond the pallet edge, and damage from handling. Engineers allow for each with safety factors. A buyer does not need the arithmetic, only to tell the supplier how the boxes will be stored and stacked, and for how long.
Reading your current box
The quickest way to know what you have is to look at the certificate on a bottom flap. It says either "edge crush test" with a figure such as 32 or 44, or "bursting test" with a figure such as 200 or 275 and a minimum combined weight of facings. That one line, with the inside size, tells a supplier almost everything about the board.
Stacking in practice
The weight rating is for one box, but a stack is the real test. A box at the bottom of a pallet four or five layers high carries all the boxes above it, for days or weeks. Plants work out the compression strength needed from the stack height and the time in storage, and allow a safety margin for humidity. If yours will be stacked high or stored long, tell us both figures.