What Is Burst strength?
Updated · Vorex Packaging
Burst strength is the amount of pressure corrugated board can take before it ruptures, measured with the Mullen test and stated in pounds per square inch. It shows how well a box resists punctures, rough handling and pressure from the contents, and it is the older way of rating shipping boxes alongside ECT.
In the Mullen burst test, a rubber diaphragm pushes against a sample of board until it bursts. The result reflects the strength of the liner papers, so it predicts resistance to punctures and impacts better than stacking strength.
When it matters
- Products with sharp corners or edges that could push through the wall.
- Heavy, dense items where the contents press on the box from inside.
- Shipments that are handled roughly, such as freight or multiple carrier transfers.
Reading the rating
Boxes rated by burst strength usually show a figure such as 200# on the box maker's certificate, the round stamp on the bottom flap, along with a gross weight limit. Boxes rated by edge crush show an ECT figure instead. Neither rating is better in general: ECT is the common choice for stacking and e-commerce, while burst strength is often specified for heavier or more fragile shipments. Ask your supplier which rating fits your product.
