Flute, ECT, and Wall Type: Choosing the Right Board for Your Box

• Flute: the wavy layer between the flat liners. Taller flutes add stacking strength and cushion. Shorter flutes give a flatter surface for print.
• ECT (Edge Crush Test): how much force, in pounds per inch, the board edge takes before crushing. Higher ECT means more stacking strength.
• Wall type: single wall has one fluted layer. Double wall has two. Triple wall has three, for heavy industrial loads.

Common flutes

Carrier rules list a maximum gross weight for each ECT grade. Use these as a floor, not a target. Confirm with your box maker before you order.

1. Weigh the packed box. Product plus inserts plus the box.
2. Count the stack. How many boxes sit on top of the bottom box in your warehouse and on the trailer?
3. Check the environment. Humid docks and cold storage cut box strength. Corrugated loses a large share of compression strength in high humidity.
4. Match a starting grade. Use the table above for weight, then size up for stacking and humidity.
5. Pick the flute. C flute for most shipping. B or E flute for print and die-cuts. Double wall for heavy or tall stacks.
6. Test the sample. Stack test in your warehouse for a week. Ship sample boxes to a real customer.

Flip the box over. The box maker’s certificate, a round stamp on the bottom flap, lists the ECT or burst rating. If the stamp is missing, ask your supplier why.

Not sure your current boxes match your load?

Send us a photo of the stamp and your stack height.

S&S Incorporated · Packaging made easy since 1965 21300 St. Clair Avenue, Cleveland, OH 44117 216-383-1880 · info@sspkg.com · www.sspackaging.com Monday–Friday, 7:00 AM–3:30 PM