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If you’ve ever had a box collapse under the weight of other packages or tear open during shipping, you know how important box strength is. Whether you’re packing, storing, or shipping products, choosing the right type of box can save you a lot of headaches. That’s where two key tests come in: Edge Crush Testing (ECT) and Burst Strength Testing (Mullen Test).
Each test measures a different type of durability, but the right choice depends on how the box will be used. And here’s something that often gets overlooked—ECT and Mullen-rated boxes are made with different types of paper liners, affecting how they perform. Let’s break it down so you can choose the right box for your needs.
Edge Crush Testing (ECT): Built for Stacking
If your boxes will be stacked on top of each other, ECT is the number to watch. This test measures how much force is needed to crush a piece of corrugated board when pressure is applied to its edge. The higher the ECT rating, the more weight the box can handle when stacked.
Why It Works for Stacking (and More!):
ECT boxes are made with fibers running north and south, meaning they’re designed to handle pressure from above. Since the fibers are aligned this way, less manufacturing goes into the paper, making ECT boxes more cost-effective.
Common ECT Ratings:
- Single-wall boxes: 23 ECT to 55 ECT (for lighter loads)
- Double-wall boxes: 48 ECT to 82 ECT (for heavier stacking needs)
Burst Strength Testing (Mullen Test): Built for Impact
If your boxes need to withstand rough handling, drops, or external pressure, the Mullen Test is the better measure. It checks how much force a box can take before it bursts, making it ideal for heavy, delicate, or irregularly shaped items.
Why It Works for Protection (and More!):
Mullen-rated boxes use a different type of paper liner than ECT boxes. Instead of fibers running in just one direction, Mullen fibers run both north-south and east-west, like a woven basket. This cross-directional fiber structure makes Mullen boxes tougher against impacts and punctures.
Because of the way the fibers are structured, these boxes can handle more unpredictable pressure from the sides, not just from stacking weight. However, the strength of a Mullen-rated box can’t be adjusted—it’s an exact measurement of durability.
Common Mullen Ratings:
- Single-wall boxes: 200#, 275#, and 350#
- Double-wall boxes: 275# and 350#
How to Pick the Right Box
- Choose ECT if your priority is stacking strength—great for warehouses and large shipments.
- Choose Burst Strength if you need impact resistance—ideal for rough handling and heavy or irregular items.
Considering shipping conditions, product weight and fragility, industry requirements and regulations, and other things is important in deciding which board type to use. The best way to find the perfect balance? Talk to and work with a packaging expert to find the ideal balance of strength, durability, and cost-efficiency.
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