| Construction | Where it is usually used |
|---|---|
| 2-wall (double wall) | Lighter loads, single trips, little or no stacking |
| 3-wall (triple wall) | The general-purpose bulk box; moderate loads, stacked a few high |
| 4-wall | Dense material such as powders, resin and metal parts |
| 5-wall | The heaviest loads, export and long storage |
ECT versus Mullen
ECT — Edge Crush Test
- Measures how much force the board takes on its edge.
- Predicts stacking performance.
- The usual specification for boxes that get stacked or stored.
Mullen — burst test
- Measures resistance to a force pushed through the board face.
- Predicts puncture and rough-handling tolerance.
- Still required by some older specs and carrier rules.
The two tests measure different things and are not directly convertible. If you are replacing a certified box, match the test it was certified against.
How to read a Box Maker's Certificate
Most certified corrugated boxes carry a round stamp on a bottom flap. It holds most of the specification.
- Board construction
- Single, double or triple wall.
- Test rating
- Either a burst test (Mullen) or an edge crush test (ECT) value.
- Size limit
- The maximum combined outside dimensions the certificate covers.
- Gross weight limit
- The maximum weight of box plus contents.
- Maker
- Who made it. Useful when you need the same box again.
A photo of that stamp sent with your quote request saves a lot of back and forth.
Flute profiles
| Flute | Relative thickness | Typical role |
|---|---|---|
| A | Thickest common flute | Cushioning and stacking; outer layers of multi-wall board |
| B | Thinner | Puncture resistance; inner layers |
| C | Between A and B | The most common shipping carton flute |
| E | Very thin | Retail and printed cartons, not bulk |
Continue through the size guide
Send a photo of the stamp
One photo of the Box Maker's Certificate helps a partner supplier match your box.
Common questions
About wall construction and strength
Is triple wall the same as 3-wall?
Yes. Triple wall corrugated has three fluted layers between four liners.
Does more wall always mean better?
No. Extra board adds cost and weight and takes up space. Match the wall count to the load and stacking.