Packaging is crushed by the weight stacked on it, not by what is inside it. The fix is board specified for the stack load and the dwell time, cases sized so pallets build square without overhang, and corner or edge protection to carry the load down the stack rather than through the carton walls.
Crushing is a stack problem
The single most useful thing to understand about crushed cartons is that the force comes from above. A carton can be entirely adequate for its own contents and collapse under four others on a pallet.
That is why specifying board against the weight of the contents - which is the intuitive approach - produces crushing. The question is what is stacked on it, how high, and for how long.
The four things that cause it
- Board specified for contents, not load. The most common cause by a distance.
- Overhang. A case extending past the pallet edge has no support under its corners, which is where the strength is.
- Part layers and poor builds. An uneven stack concentrates load unpredictably.
- Moisture and dwell. Board loses compression strength as it absorbs moisture and over time; a stack stable at despatch can fail after weeks in a humid building.
Corners carry the load
A carton's compression strength is concentrated at its vertical corners, not in the middle of its walls. Everything that preserves corner alignment preserves strength.
| Measure | Effect |
|---|---|
| Cases sized to the pallet footprint | No overhang; corners supported by the case below |
| Square, aligned stacking | Corners load onto corners |
| Corner boards | Transfers load vertically down the stack |
| Correct wrap tension | Unitises without pulling the stack out of shape |
| Consistent layer pattern | Predictable load paths |
| Column stacking where possible | Stronger than interlocked for compression |
What protects the corners.
Corner boards are frequently cheaper than a grade up in board and address the cause more directly. See industrial packaging.
Specifying board for the real load
- Establish stack height - how many cases high, in your warehouse and at the customer's.
- Establish the weight of everything above the bottom case.
- Establish dwell time and storage conditions, including humidity.
- Specify board to carry that load over that period, not just to hold the contents.
- Sample and test a full stack before committing.
See packaging materials for the board constructions.
Moisture is the hidden variable
Corrugated board loses a significant proportion of its compression strength as it takes up moisture from humid air. A stack that was comfortably within tolerance at despatch can be marginal after a fortnight in an unheated warehouse or a sea container.
If goods dwell, or travel by sea, allow for it explicitly - a higher grade, a moisture barrier, or both. See export packing.
Where it shows up and what to check
- Bottom layer crushed - classic stack load. Check board grade and stack height.
- One side crushed - likely overhang or an uneven build.
- Crushing after storage rather than transit - dwell and humidity.
- Crushing started recently - check whether board grade, supplier or stack height changed.
The cheaper fixes first
Before upgrading board across the range - which costs on every unit - check the cheaper structural options: case sizing to remove overhang, corner boards, a different layer pattern, or simply stacking one lower.
Those frequently solve it for less. If they do not, then the board grade genuinely needs revisiting - see packaging review and cost reduction.
The short version
- The force comes from above, not from inside.
- Compression strength is concentrated at the vertical corners.
- Overhang removes corner support entirely.
- Board loses strength with moisture and dwell.
- Try the cheap structural fixes before upgrading board across the range.
Frequently asked questions
Why do our boxes crush at the bottom of the pallet?
Because the board was specified for the contents rather than the load above. Check stack height and total weight above the bottom case.
Will double wall fix it?
Often, but check the cheaper options first - overhang, corner boards and build quality frequently solve it without a cost on every unit.
Why does it only happen after storage?
Board loses compression strength as it absorbs moisture and over time. Long dwell in a humid building is a common and overlooked cause.
Does stacking pattern matter?
Yes - column stacking is generally stronger in compression than interlocked, because corners load onto corners.
Can WSUK specify this?
Yes - send stack heights, weights, dwell times and storage conditions and we will specify the board and the protection. See industrial packaging.