There is a simple test you can do with a PP honeycomb panel and no equipment. Stand it on edge and press the middle with your thumb. Then lay it flat and press the same spot. The difference is enormous, and it is the whole reason honeycomb works — and the whole reason orientation has to be specified rather than assumed.
The two directions are not similar
In a honeycomb panel the cell walls are columns between the two skins. Load applied perpendicular to the skins travels down those columns and is resisted by the walls in compression, which they do very well. Load applied along the plane of the panel pushes the columns sideways, and they buckle at a tiny fraction of that load.
So the panel is extremely stiff in bending — like a flat plate — and comparatively weak in flat-wise shear or edge loading. Neither of those is a defect. They are the properties you are buying. But a rack application puts the panel into a specific load case, and if the installation does not match it, the panel will not deliver what the datasheet promises.
Three common racking situations
Panel as a shelf deck
This is the good case. The panel spans between rack beams with the skins horizontal and the cells vertical. Bending load is exactly what the structure is built for, and a panel of modest thickness will carry a distributed load across a respectable span with minimal deflection.
The thing to check is the span. Deflection grows with the cube of the unsupported distance, so doubling the span roughly multiplies sag by eight. Shorten the span or step up thickness — the second option costs less than people expect because stiffness scales so strongly with thickness.
Panel as a vertical divider
Dividers see edge loading and flat-wise pressure rather than bending. Here the cells run horizontally, which is the weak direction, and the panel relies on the frame around it to take the load. Used as a divider between stacked goods inside a box, that is fine — the load path goes through the goods and the container walls, not through the panel.
Used as a freestanding vertical barrier with goods leaning on it, it will bow. If you need a self-supporting partition, the panel needs a perimeter frame or it needs to be thick enough that the skins carry the load in bending.
Panel as a pallet top sheet
Between the load and the pallet deck, a top sheet sees distributed compression, which it handles well, plus point loads from the pallet deck boards underneath. The cells bridge the gaps between boards and spread the load — this is one of the most cost-effective uses of the material, and it works because the load path is compression through the cells.
The failure mode to watch is a heavy, small-footprint item sitting on a thin sheet over a wide gap between deck boards. That is a bending case in disguise, and a 5 mm sheet may not be enough where a 10 mm one would be.
Point loads are the real enemy
Whatever the orientation, concentrated loads are what damage honeycomb. A pallet truck fork tip, a rack beam edge, a castor wheel, the corner of a steel bracket — any of these can crush cells locally and start a dent that grows.
The countermeasures are boring and effective: spread the load with a layer pad or a wear plate, round off whatever is pressing, or specify a higher-density core in the zones that take the contact. The last one is worth asking about, because density can be varied across the panel rather than everywhere.
What to put on the drawing
- Orientation of the cells relative to the installed position, with a sketch
- Support span and the load distribution — uniform, line, or point
- Panel thickness, and whether the load is static or cycling
- Temperature, because polymer stiffness falls as temperature rises and a panel that is fine at 20°C may sag in a sunlit warehouse
That last line catches people out. Creep under sustained load at elevated temperature is the reason a shelf that looks perfect on day one has a visible dip by month six. If the load is permanent rather than intermittent, derate the capacity meaningfully or specify a thicker panel.
A quick sanity check before you order
Ask the supplier for the panel’s behaviour in your actual configuration — span, load, temperature, duration — rather than a general compressive strength figure. A supplier who has made panels for racking will answer with a deflection number and a time factor. A supplier who has not will answer with a datasheet.
Orientation is a one-line specification that costs nothing to get right and is the single most common reason a honeycomb panel underperforms in service.