32-ECT vs. 200# Mullen Test: What the Numbers on a Box Actually Mean

A box stamped 200# test sounds tougher than one stamped 32-ECT. Bigger number, stronger box, right? Not quite. They're two different tests that land on the same grade of single-wall corrugated, and the numbers can't be compared directly.

BOXT stocks 32-ECT single-wall boxes in Spanish Fork for same-day pickup and delivers across the Wasatch Front next-day or same-week. Outside Utah, expect most orders in 3–5 business days.

What the Mullen (Burst) Test Measures

The Mullen test, also called the burst test, measures how much pressure it takes to rupture the board. A machine pushes a rubber diaphragm into a sample until the facing breaks, and the result is in pounds per square inch. A 200# test board bursts at 200 psi.

That tells you about the board's resistance to puncture and rough handling. It says much less about how a box holds up under a stack.

What ECT (Edge Crush Test) Measures

ECT takes a short strip of board, stands it on its edge, and compresses it until it crushes. The result is in pounds per inch of edge length, so 32-ECT means the board resists 32 lbs per inch of edge before it fails.

That matters because a stacked box is loaded straight down through its walls. ECT is a better predictor of stacking strength, and it's why most buyers now spec by ECT.

Are 32-ECT and 200# Mullen the Same Box?

For single-wall corrugated, they're generally treated as equivalent grades. Check the box maker's certificate, the round stamp on the bottom flap, and you'll see either a burst rating or an ECT rating along with size and weight limits. Both are accepted, but they're different units: 200 psi of burst versus 32 lbs per inch of edge crush. The numbers aren't a ranking of which box is stronger.

Three Common Myths

• "200 is bigger than 32, so it's stronger" — different units, different tests. There's nothing to compare numerically.
• "Higher burst means better stacking" — not necessarily. Heavier facings can raise a burst number while the flute still crushes under a load.
• "Stronger is always better" — over-spec'd boxes cost more to buy and more to ship. Match the grade to the load.

Flute Matters Too: B vs. C

ECT is a property of the whole board, and the flute is part of it. Two common single-wall flutes:

• B flute — thinner, at roughly 1/8 inch. A firmer, flatter surface that resists crushing and takes print well.
• C flute — thicker, at roughly 5/32 inch. More cushioning and better vertical stacking strength.

Our 32-ECT Corrugated Boxes

Our standard 32-ECT corrugated shipping boxes are single-wall, industry-standard RSC construction in B or C flute, kraft finish, and they ship flat for efficient storage. They're built for e-commerce, distribution and general warehouse use, where you want consistent strength at a cost that scales.

As a rule of thumb, single-wall 32-ECT suits products up to roughly 65 lbs gross weight. Heavier loads, or boxes that get stacked high, are where double wall comes in.

How to Choose the Right Grade

• Product weight — start here. Heavy contents push you toward a higher grade.
• Stack height and dwell time — boxes on the bottom of a tall stack, or stored for weeks, need more edge crush than boxes shipped out the same day.
• Shipping method — parcel handling punishes corners and sides, while pallet freight punishes stacking strength.
• Humidity — moisture softens corrugated and lowers effective strength, so storage conditions count.

For a wider look at what we carry, see our corrugated shipping boxes guide.