Why Containers Crack in Transit: Stacking and Breakage

What actually fails

Three failure modes, in order of frequency:

Rim cracking is the one that surprises buyers. The container arrives intact-looking, then splits the moment it is flexed — because the rim took a load it was not designed for and micro-cracked.

The arithmetic of stacking

A 40HQ interior height is about 2.69 m. Pallet height 1.8 m plus pallet base 0.15 m gives two tiers — that is normal and safe. The problem starts when a warehouse stacks cartons loose to 2.5 m to use the last 20 cm.

Take PF-SQ750: 300 pcs per carton, 7.2 kg gross, carton 52.5×25×35.5 cm.

• Floor-loaded to 2.69 m: 7 cartons high
• Bottom carton carries 6 × 7.2 kg = 43.2 kg on a 52.5×25 cm footprint
• That is about 330 kg/m² of static load

Standard single-wall corrugated handles 400–600 kg/m² when new and dry. It handles less after 30 days at 80% humidity, and less again after a sea crossing. A 7-high floor load is at the edge, not comfortably inside it.

The four levers

1. Stack height. Cap at 5 cartons for anything above 6 kg gross. The lost volume is about 20%, but the breakage claim is usually larger.

2. Carton grade. Moving from single-wall to double-wall at the base costs a few cents per carton and roughly doubles compression strength. For long sea routes, specify it.

3. Palletising. A pallet spreads the load and removes the human variable. Two pallets high is safe; three is not, for PP.

4. Container position. Cartons near the door take the most handling. Put the heaviest, most fragile SKUs at the far end.

Heat is the second killer

A closed steel container in direct sun at Jebel Ali or Lagos reaches 60–70°C inside. PP softens around 100°C, so it does not melt — but a thin-wall container at 0.5 mm will warp at the rim under its own stack load.

Two practical countermeasures:

• Ship below deck or in a ventilated container for thin-wall items in summer lanes
• Reduce stack height for thin-wall SKUs — PF-RW300 at 11 g and PF-SQ750S at 19.5 g are the thin end of this catalogue and the most heat-sensitive

Reading a damage claim

When a buyer reports breakage, three questions separate a packaging problem from a product problem:

1. Which layer? Bottom layer means compression. Random layers mean handling.
2. Which part? Rim means stacking. Corner means impact. Lid means heat.
3. What percentage? Under 1% is normal transit loss on a floor-loaded container. Above 3%, something in the packing design is wrong.

Photos of the carton, not just the container, are what make a claim actionable.

What to specify to prevent it

FAQ

Are PP containers fragile? Not in normal use. They are fragile under sustained compression and at the rim. A dropped container usually survives; a crushed one cracks later.

Does a thicker wall prevent breakage? It helps at the rim, but a 40 g container in a badly stacked carton still cracks. Packing design matters more than wall thickness.

Should I buy corner protectors? For palletised loads, yes — cheap and effective. For floor-loaded cartons, they add handling time and rarely help.

Who pays for transit damage? Whoever holds the risk at that point in the Incoterm. Under FOB, the buyer after loading; under CIF, still the buyer, but with insurance. Photograph the container seal at loading — it is the only evidence that separates pre-shipment from in-transit damage.

Related reading

• 300–500ml Small PP Container: Which Size for Sides
• 16oz PP Deli Container: PF-520 470ml Specifications
• 750ml PP Food Container: 9 Models Compared

Models covered on this site: 750 ml PF-L750 · 2500 ml PF-RW2500 · 1000 ml PF-RW1000 · see all models in this category.