Corrugated board and boxes are given two types of tests to determine their durability and strength: the ECT, or Edge Crush Test, and the burst, or sometimes called “Mullen,” test. These tests are completely different and measure different properties of the material.
In simple terms, the ECT measures top-to-bottom compression strength, while burst measures primarily puncture and tear resistance. The following is taken from the ISTA (or International Safe Transit Association) website, and describes the two grading systems in more detail:
“Corrugated grades are based on these tests. When a test is applied to a sample, then the results allow us to assign a grade. So a particular run of board is not intrinsically ECT or burst, the designation only refers to how it was tested (board may be designed to optimize one or the other test results, however). If a run is designed to be graded ECT and then is graded ECT and marked accordingly, we typically call it ECT grade board. But the sample run could also be graded burst. Grade is just a classification system and there happens to be two systems. Accordingly it is not typically possible to tell the difference between ECT and burst grades as all board can fit into both grading systems.”
So if your primary concern is crushed boxes and stacking problems, consider specifying in terms of ECT. If it’s containment strength and puncture resistance, consider specifying in terms of burst. If you need both, specify both.
Approximate ECT to Mullen Conversion Chart:
Numbered Packages: Where Numbered Package descriptions specify boxes, containers, trays, and component parts thereof to be made of corrugated fiberboard having a minimum bursting or puncture test as shown in Column A below, boxes, containers, trays, and component parts thereof may be made of corrugated fiberboard having a minimum edge crush test as shown in Column B below. These alternate provisions will exempt basis weight requirements.
Minimum Bursting Test
Singlewall and Doublewall Board (psi)
or Minimum Puncture Test Triplewall
Board (inch oz. per inch of tear)
Minimum Edge Crush Test (ECT)
(lbs per inch width)
Source: Fibre Box Handbook ©2010