Wood packaging that carries an ISPM 15 mark must be made from debarked wood. The standard does not demand a perfectly clean surface: small, discrete patches of bark may remain if each piece is under 3 cm wide, or, if wider than 3 cm, has a surface area under 50 cm². The rule exists because bark and the layer beneath it are where most wood-boring insects live, feed and lay eggs.
What the standard actually says
ISPM 15, Regulation of wood packaging material in international trade, is the international phytosanitary standard published under the International Plant Protection Convention (IPPC). It requires wood packaging material (WPM) to be debarked and then treated with an approved measure, usually heat treatment, and marked.
Paraphrasing the 2009 text, any number of separate pieces of bark may stay on the wood if either condition holds:
- the piece is narrower than 3 cm (1.2 in), however long it is; or
- the piece is wider than 3 cm, but its total surface area is less than 50 cm² (7.75 in²).
The test applies to each individual piece of bark, not to the pallet as a whole. A pallet with a dozen small, separate patches can therefore comply, while a single strip of bark 4 cm wide and 15 cm long (60 cm²) does not.
| Bark piece | Width | Area | Compliant? |
|---|---|---|---|
| Narrow strip along a board edge | 2 cm × 40 cm | 80 cm² | Yes (width under 3 cm) |
| Square patch on a stringer | 5 cm × 5 cm | 25 cm² | Yes (area under 50 cm²) |
| Wide patch on a block | 6 cm × 9 cm | 54 cm² | No |
| Long wane strip with bark | 4 cm × 15 cm | 60 cm² | No |
Debarked is not the same as bark-free
The wording matters. Some national plant protection organizations and many customers use "bark-free" informally, but ISPM 15 uses "debarked". Debarked means that the bulk of the bark has been removed in a process that produces clean wood; it does not require the removal of the inner bark or the vascular cambium in every last corner. Round or wane-edged boards, where the log's curved outer surface meets the sawn face, are the usual place where tolerated bark remains.
The practical consequence is that producers should treat the 3 cm and 50 cm² limits as an upper bound, not a target. Bark fragments close to the limit are easy to dispute at the border, and an inspector measuring a doubtful patch will not give the benefit of the doubt to a pallet that already looks untidy.
Why bark matters phytosanitarily
Bark is the preferred habitat of many of the insects that ISPM 15 was written to stop. Bark beetles feed in the inner bark and cambium, and several longhorn beetles lay eggs in bark crevices before their larvae tunnel into the wood.
There are three reasons the standard handles bark separately from treatment:
- Treatment reaches bark less reliably. Heat and fumigant behave differently in bark and in the thick, resin-rich wood underneath it.
- Bark can hold pests that treatment kills but that leave residues such as frass, galleries and dead insects. These are visible evidence and can trigger a rejection even when the insects are dead.
- Reinfestation is possible after treatment. Wood that retains bark is more attractive to beetles that arrive after treatment but before the cargo ships.
The pests behind these rules include the pinewood nematode, carried by Monochamus longhorn beetles that breed under pine bark, and the Asian longhorned beetle, both of which spread internationally on untreated packaging.
When debarking must be done
The standard sets the timing by treatment type:
| Treatment | When debarking is required |
|---|---|
| Heat treatment (HT) and dielectric heating (DH) | Debarking may be done before or after treatment |
| Methyl bromide fumigation (MB) | Wood must be debarked before treatment |
The reason for the stricter rule for fumigation is that gas does not penetrate bark well, so bark must come off before the wood is exposed. Because methyl bromide is being phased out in many markets, most producers use heat treatment, where the order is a matter of workflow rather than compliance.
In most pallet plants, debarking is not a separate step at all. Logs are debarked at the sawmill, usually in a ring or rotor debarker before sawing, and the lumber that arrives at the pallet plant is already clean. Producers who buy rough, wane-edged lumber or cut their own timber have to check and trim residual bark before treatment.
Controlling bark in a pallet plant
Plants that make marked pallets typically combine several controls:
- Specify bark tolerance in lumber purchase contracts, citing ISPM 15 and, if useful, a lower internal limit.
- Inspect incoming loads for bark, particularly on stringers, blocks and the edges of deck boards cut from slabs.
- Trim at the cut-off or notching station. A small bark patch on a wane edge is often removed by a trim saw or notching machine; see cut-off and trim saws.
- Check again after treatment and before marking. A final visual check at the stamping station catches boards that slipped through.
- Record the checks as part of the plant's compliance records, which an auditor from the national plant protection organization (NPPO) or an accredited agency may review; see the ISPM 15 certification process.
How inspectors treat bark
Importing countries apply the standard through their own inspection services. Australia's import conditions, for example, require compliant packaging to meet the ISPM 15 bark tolerance requirements, and consignments that fail can be sent for treatment, export or destruction at the importer's expense. In the European Union, WPM that does not meet ISPM 15 can be detained, re-exported or destroyed under the official controls framework.
Because the rule is a visual one, enforcement depends on the inspector's judgment and the measuring tools available. A transparent grid or a ruler is enough to check the 3 cm width; the 50 cm² area is checked by approximating the patch as a rectangle.
Frequently asked questions
Does ISPM 15 require pallets to be completely bark-free?
No. The standard requires debarked wood and allows any number of separate bark pieces that are narrower than 3 cm, or wider than 3 cm with an area under 50 cm² each.
Does the bark rule apply to plywood or OSB pallets?
Not in the same way. Wood packaging made wholly of processed wood such as plywood, OSB or veneer is outside the scope of ISPM 15, so neither the treatment nor the bark rule applies. See ISPM 15 exemptions.
Can bark be removed after heat treatment?
Yes. For heat treatment and dielectric heating, ISPM 15 allows debarking before or after treatment. For methyl bromide fumigation, the wood has to be debarked first.
Is bark that falls off during transport a violation?
Loose bark that has detached is not a measurement against the tolerance, but live insects, frass or galleries found in the wood can still lead to action regardless of the 3 cm and 50 cm² limits.
Sources
- ISPM 15: Regulation of wood packaging material in international trade (2009) — International Plant Protection Convention (FAO)
- ISPM 15 import requirements for timber packaging — Australian Government Department of Agriculture, Fisheries and Forestry
- EU import requirements for wood packaging material, explained — Agrinfo.eu
- Wood Packaging Material — USDA APHIS
- Wood Packaging Material Enforcement Regulations (November 2025) — American Lumber Standard Committee