Understanding the Strength of a Box
ECT VS. Mullen - You Be The Judge
There are varying thicknesses (single wall, double wall, triple wall, etc.), several different flute types (A, B, C, E, F, etc.), and a wide variety of papers that can be used in corrugated construction.

All of these factors determine the strength and durability of the carton. Too weak, and the carton may collapse or puncture. But too strong, and you’re paying for material you don’t need.

When choosing the proper corrugated carton from an environmental standpoint selecting a properly sized carton can make a very big difference. Using post-consumer recycled content is another important consideration. But even cartons with high levels of post consumer content require energy and create pollution in their manufacture, so reducing the total amount of material used is an important consideration. Besides reducing carton size, another waste prevention strategy is to avoid purchasing cartons that are overly protective.

There are currently two tests used throughout the corrugated industry to determine strength. Historically, the long time industry standard has been the Bursting (Mullen) Test, which is related to the rough handling durability of corrugated material. Bursting Test is a measure of the force required to rupture or puncture the face of corrugated board and is measured by a Mullen Tester. This force is indirectly related to a carton’s ability to withstand external or internal forces and thus to contain and protect a product during shipment. Bursting strength is reported in pounds (for example, 275#).
A newer standard that has achieved widespread acceptance is the Edge Crush Test (ECT). This is a true performance test and is directly related to the stacking strength of a carton. ECT is a measure of the edgewise compressive strength of corrugated board. It is measured by compressing a small segment of board on edge between two rigid platens or plates perpendicular to the direction of the flutes until a peak load is established. This is measured in pounds per lineal inch of load bearing edge (lb/in), but usually reported as an ECT value (for example, 44 ECT).

A way to be sure the material of the box you are purchasing meets industry standards is to look for the Manufacturer's Certification Stamp, usually printed on one of the bottom flaps of the box. The stamp identifies the material as "singlewall," "doublewall" or "triplewall." It also certifies the Mullen Bursting Test ( most common is 200 lbs. per square inch) or the Edge Crush Test (ECT 32 lbs. per inch). The Mullen Test measures the bursting strength of the corrugated linerboard while the Edge Crush Test measures linerboard stacking strength.

The 200 lbs. Mullen box and the 32 ECT box are comparable in stacking strength. But that is where the similarity ends. The Mullen Test box is better suited for the protection of heavier contents while the Edge Crush Test box provides lighter weight cartons with good stacking characteristics. When in doubt as to which box to use, always select the Mullen Test box because the construction of the linerboard cannot be altered. For example, 200# Mullen Test linerboard must be made of 42# per square inch basis weight paper and the medium or flute paper cannot be less than 23# per square inch basis weight.