Ask ten importers what went wrong on their last damaged shipment and nine will describe a machine problem. Read the receiving report and the cause is usually a carton that was never specified, on a pallet that was never designed, loaded against a wall.
Packaging is the only part of an auto parts order that a buyer can specify completely, at low cost, before production begins. An auto parts packaging specification costs nothing to write and is also the part most often left to an assumption.
Start With the Drop and Stack Test
Two physical tests determine whether a specification is adequate, and both are cheap enough to require on a sample shipment.
The drop test answers whether a carton survives a single handling event at the destination warehouse. The stack test answers whether it survives six weeks of static load in a container.
| Test | Method | Pass condition |
|---|---|---|
| Drop, single carton | ISTA 3A, 6 faces, 76 cm | No part exposure, no deformation beyond 5 mm |
| Stack, 30 days | 1.8 m stack at 38 C, 85% RH | Carton height loss under 4%, contents undeformed |
| Vibration | ISTA 3E, 2 hours random | No abrasion through inner protection |
| Compression | ASTM D642, edge crush | Retains 60% of initial strength after humidity |
The humidity condition in the stack test is the one buyers skip, and it is the one that matters on a sea freight leg. Corrugated board loses roughly half its compression strength at 85% relative humidity, which is why a carton that passed in a dry warehouse fails in a container.
Thirty days at 1.8 m is a deliberately conservative substitute for a six-week voyage. If a carton passes at those values, the loading plan has margin rather than luck.
Inner Packaging: What to Specify Per Part Family
Inner protection is not a generic requirement. It varies by failure mode, and a specification that does not name the failure mode is not a specification.
| Part family | Dominant risk | Specify |
|---|---|---|
| Brake discs and drums | Hub face deformation, rust | VCI paper plus edge protector, no stack over 0.9 m |
| Brake pads | Shim abrasion, friction face contamination | Foam separator per set, sealed bag per set |
| Filters | Media crush, seal distortion | Moulded pulp or corrugated insert, no nesting |
| Sensors and electronics | ESD, connector damage | Anti-static bag, connector cap, foam cradle |
| Bearings | Contamination, brinelling | Vacuum bag, individual box, no shock load |
Brake discs illustrate the point. The dominant risk is not impact but static load on the hub mounting face, which produces runout that only appears after installation and is therefore attributed to the vehicle rather than the packaging.
Bearings fail differently again. Brinelling from shock load does not show at receiving and does not show at installation, but it produces noise within a few thousand kilometres and is almost never traced back to a carton.
Carton and Pallet Specifications
Four values turn a carton description into a specification that a factory can be held to.
- Board grade as ply count plus edge crush test value, not as a trade description such as 'export grade'.
- Internal dimensions with a tolerance, since a 5 mm variation changes whether a part moves inside the carton.
- Pallet standard: 1200x1000 or 1200x800, with the pattern and overhang limit stated.
- Maximum stack height in metres, stated per part family rather than per shipment.
Edge crush test value is the single most useful number on that list. It is measurable, it is comparable between suppliers, and it predicts compression performance far better than a ply count alone.
Stating stack height per part family rather than per shipment is what makes a loading plan possible. A single number for a mixed container forces the stevedore to guess, and stevedores guess upward when they are short of space.
Container Loading: Weight, Height, and Securing
Loading is a design task with three hard constraints and one soft one, and the soft constraint is the one that causes damage.
| Constraint | Limit | Common error |
|---|---|---|
| Payload | 26.5 t for a 40HQ | Declared gross weight omits pallet weight |
| Internal height | 2.69 m | Assuming 2.9 m from a general figure |
| Floor positions | 20 standard, 24-25 Euro | Planning to the volume figure instead |
| Securing | No gaps over 10 cm at the door | Inflatable dunnage omitted on a part load |
Payload errors are quietly common because pallet weight is frequently left out of the declared gross. Twenty-five Euro pallets at 22 kg each is over half a tonne that nobody counted.
Securing is where partial loads fail. A container at 70% fill has a gap at the door, and every braking cycle on the road leg moves the load toward it until the cartons at the front take the accumulated force.
Inflatable dunnage solves most of it for a few tens of dollars. Requiring a photograph of the secured load before the doors close costs nothing and settles the argument later.
The Clauses Worth Writing
A one-page packaging annex on the purchase order removes most of the ambiguity that damage claims are built on.
- Board grade, edge crush test value, and internal dimensions with tolerance.
- Inner protection named per part family, with the failure mode it addresses.
- Drop and stack test values, with a test report required before first shipment.
- Pallet standard, pattern, overhang limit, and maximum stack height.
- Loading photographs required before the container doors close.
- Claim window and evidence standard, agreed before the first order.
The claim window clause is the one buyers most often forget. Without it, a damage claim raised eight weeks after discharge becomes a negotiation about timing rather than about cartons.
Agreeing the evidence standard in advance matters just as much. A photograph with a scale reference and a carton grade written on the packing list is evidence; a description of crushed boxes is an opinion.
Frequently Asked Questions
Is a carton upgrade always worth the cost?
No. It is worth it where the part is stack-loaded, humidity-exposed, or surface-critical. For light, non-critical parts in a single-tier load, a standard carton with good inner protection is sufficient and cheaper.
Who should pay for packaging testing?
The supplier, provided the test standard is named in the purchase order. Test reports for drop and stack are inexpensive relative to the cost of a single rejected container, and most factories already run them for other customers.
How much does humidity actually reduce carton strength?
Corrugated board can lose around 50% of its compression strength at 85% relative humidity, depending on grade and coating. This is why a stack test run in a dry warehouse predicts nothing useful about a sea freight leg.
What is the minimum useful loading specification?
Pallet standard, maximum stack height per part family, payload including pallet weight, and a requirement for securing photographs. Those four items prevent the majority of partial-load damage.
Reference Sources
ISTA 3A — Packaged products for parcel delivery system shipment.
ISTA 3E — Unitized loads of similar products for truck and rail.
ASTM D642 — Compressive strength of shipping containers.
GB/T 6543-2008 — Corrugated fibreboard boxes for transport packaging.
CTU Code 2014 — IMO/ILO/UNECE Code of Practice for Packing of Cargo Transport Units.
ISO 668:2020 — Series 1 freight container classification and dimensions.