Guide
Box compression strength, explained
Box compression strength is the top load a box carries before it buckles. Humidity, cold and time all cut it.
Box compression strength is how much load a box carries on top before it buckles. In a box compression test a platen presses the box until the load climbs, peaks and then drops. That peak is the number, and it moves with humidity, temperature, time and pallet overhang. The Twin Cities swing through all four each year.
Four things that cut it
| Cause | What the sources say | What we plan |
|---|---|---|
| Humidity | About half the compression strength is lost from 50% to 90% relative humidity (Fibre Box Handbook, via PaperIndex) | 50% in covered outdoors, 55% in a cooler |
| Time under load | Nearly 45% lost after 90 days in humid conditions (AICC) | 55% past 90 days, 70% to 90 days, 85% to 30 days |
| Cold | Cold makes board stiffer and more brittle; adhesives can lose effectiveness (AICC) | 60% to 65% on a dock, trailer or in a freezer |
| Overhang | Strength decreases as overhang increases (Virginia Tech) | 80% if the box hangs over the pallet |
The margin for a used box
New board is the baseline. A used box has been loaded, handled and stored, so it starts lower. Those are our planning shares, not published figures; they are chosen to be conservative and are shown in Stack Check.
Why ECT matters more than wall count
The edge crush test, ECT, rates the board by how much load an edge carries. It is the rating that best predicts how much top load a box carries in a stack. Wall count is a proxy: more layers, more board. The Cary Company pairs 1100# triple wall with ECT-90 and its heavy octagon with ECT-155. See the ECT guide.
What to do about it
- Store gaylords in heated areas above 55 F when you can.
- Do not leave loaded stacks standing for months; rotate them.
- Keep boxes off wet floors and out of the weather.
- Square the stack on the pallet. Overhang costs strength.
- Let cold boxes reach room temperature before you open them.
Next: winter docks and condensation and how high to stack.
Where to see this on your own dock
Look at the bottom box of any stack that has stood a month. If its walls bow near the middle, the box is already telling you it is at its limit. If the corners are rounded or the flaps have lifted, the stack is past it. These signs show up long before a collapse and give you the chance to unstack in time.
Questions, answered
What is box compression strength?
The top load a box carries before it buckles, measured by pressing a platen onto it. The peak of the load curve is the number.
Does humidity weaken cardboard boxes?
Yes. Corrugated loses about half its compression strength when relative humidity rises from 50% to 90%.
Sources and last reviewed
Facts on this page were last reviewed 2026-11-11.
- PaperIndex Academy: humidity and corrugated strength: How corrugated board loses compression strength as relative humidity climbs from 50% to 90%.
- AICC: strengthening corrugated against cold weather: Industry guidance on cold weather, condensation between temperature zones, and strength lost over 90 days under load.
- Virginia Tech: pallet overhang and box compression strength: University research on how pallet overhang lowers box compression strength.
- The Cary Company: gaylord boxes, history and handling: A packaging distributor's history of the gaylord and its board ratings by wall count.