If you have ever been shopping for corrugated boxes for your warehouse, dock, or shipping operation, you may have noticed that they come rated at various weight tests.
For example, you might find corrugated boxes that are 250 lb. test or 350 lb test. But what does this actually mean? Can you really put 250 or 350 lbs. of products, parts, or other items in there and they won’t fail?
Corrugated Box Mullen Tests
There are basically two different tests used to measure the strength and durability of corrugated boxes. The first is the Mullen Test, also known as the bursting test.
The Mullen Test measures the rough handling durability of the corrugated material. It’s actually a measure of the force required to rupture or puncture the face of the corrugated cardboard material. A special tool known as a Mullen Tester applies force to the carton until it actually splits or bursts. This weight is its test weight, such as 275 lbs., for example.
Edge Crush Test
Now there is a second test that is used to measure the durability of corrugated boxes. The Edge Crust Test — or ECT, for short — is related to the stacking strength of a carton.
The ECT measures the edgewise compressive strength of corrugated board by compressing a small segment of the board on edge between two rigid platens or plates that are perpendicular to the direction of the flutes. The purpose of this is to establish a peak load, which is measured in pounds per lineal inch of load bearing edge.
But the ECT is usually expressed as an ECT value: For example 44 ECT.
Minimum Values
The ECT values are a minimum value. This is because manufacturers of corrugated boxes may use different “recipes” when creating their corrugated cardboard materials, each of which may vary slightly in overall strength.
For example, a 200 lb test box may have an ECT that could be anywhere from 32 ECT to 44 ECT. The difference has to do with the amount of material that is used. Corrugated materials with lower ECTs may use fewer raw materials, have lower energy requirements, create less pollution to make, and so on.
Using lighter materials to make a container that is the proper size for the item being shipped with increasing amounts of recycled content is better for the environment. But that doesn’t help if the box isn’t strong enough to hold what’s inside.
If the corrugated boxes you are using are likely to undergo rough handling, a bursting strength rating is a better measure than ECT, in general.