Palletisation

There are two ways to stack boxes, and they are in direct opposition. Column stacking places each box squarely on the one below, corner over corner, so load runs straight down through the strongest parts of every package to the pallet. It preserves nearly all the compression strength the cartons have. It is also unstable: nothing ties one layer to the next, and the stack relies entirely on external securing to stop it shearing apart.

Interlocking, or brick, stacking rotates alternate layers so boxes bridge across the joints below, tying the stack together. It is far more stable and it is what a person unfamiliar with the problem naturally does. It is also structurally destructive: a box whose corners land in the middle of the panels below has nothing under its corners. The corner load goes into an unsupported span, panels deflect, and a substantial share of the stack's theoretical strength is thrown away — often a very large share.

So palletisation is a real trade rather than a best practice: column for strength and secure it externally, or interlock for stability and specify heavier packaging to survive it. Both answers are defensible. What is not defensible, and is extremely common, is interlocking a stack of cartons specified on the assumption of column stacking, and then discovering the failure at the destination.

Forced-air cooling depends on a continuous path for air from one side of the pallet to the other, and that path exists only if the vents of every package line up with the vents of its neighbours, layer after layer, all the way through. Air takes the easiest route available: offer it a gap around the outside of the pallet and it will go there rather than through the resistance of a fruit-filled box. The result is a pallet whose outer cartons cool nicely and whose centre stays at field temperature for days, while the store's instruments report that the room is at temperature and everything is fine.

This is where the interlocking decision does its second piece of damage. Rotating alternate layers rotates their vents too, so a pattern chosen for stability blocks the vertical and horizontal air paths almost by definition. It also makes the failure invisible: nothing about the outside of the pallet indicates that its middle is warm. Add a pallet wrapped tightly in unperforated stretch film — applied for stability, as a separate and reasonable decision — and the block is sealed on all four sides. Two individually sensible choices, made by different people for different reasons, combine into a pallet that cannot be cooled at all.

Overhang

A package projecting past the pallet edge has no support under its outer corners, and the strength lost is out of all proportion to the small overhang that causes it. Underhang — a footprint smaller than the pallet — wastes space but is structurally harmless.

Pallet condition and deck gaps

A package spanning a gap between deck boards is unsupported where it most needs support. Broken boards, protruding nails, and warped pallets damage the bottom layer and destabilise everything above it.

Securing

Stretch film, strapping, corner boards, and adhesives hold the unit together, and each does something different. Film resists shear and does nothing for compression; corner boards carry vertical load and can restore some of what the pattern took away.

Layer pads and slip sheets

Sheets between layers spread load across the packages below and stop boxes settling into the gaps between the boxes beneath, which is a common route to progressive collapse.

Load height and centre of gravity

Tall pallets are more prone to toppling in handling and cornering, and a heavy layer high in the load makes it worse. Stability in motion is a different problem from stability at rest.

The platform itself carries obligations that have nothing to do with the produce. Wooden pallets are solid-wood packaging material, and in international trade they are subject to plant-health treatment and marking requirements, because timber carries forest pests between continents. A consignment can be stopped at a border because of the pallet under it. Plastic and pressed-composite pallets avoid that entirely, which is a substantial part of why they exist despite costing more.

Pallets are also pooled and exchanged, which makes them a returnable-packaging system with all the properties that implies: they must come back, they need repair, they are lost, and they are quietly repurposed. A pooled standard footprint is what allows a pallet to travel through many parties' equipment at all — and it means the pallet's dimensions, not the produce's, set the geometry that cartons and crates must fit. The package sizes seen throughout the produce trade are largely a consequence of what divides neatly into a pallet footprint.