How to read the HT stamp on a pallet
The HT stamp is a mark burned or inked into a pallet to show its wood was heat treated to the ISPM 15 standard. It means the core of the wood reached at least 56 degrees Celsius for at least 30 minutes.
What each part of the mark says
| Part | What it shows |
|---|---|
| IPPC symbol | That the treatment follows the International Plant Protection Convention standard |
| Country code | Where the wood was treated; two letters, for example US |
| Producer number | Which facility treated or made the pallet |
| HT | Heat treatment: wood core reached at least 56 °C (133 °F) for at least 30 minutes |
| MB | Fumigation with methyl bromide, the other approved route |
| DB | Debarked, a required step before heat treatment or fumigation |
| DUN | Wood intended as dunnage, not as a manufactured packaging unit |
Debarking and the bark rule
Wood packaging has to be debarked before treatment to meet ISPM 15. A little bark can remain: strips under 3 centimetres wide are allowed, and wider patches must cover less than 50 square centimetres.
What the stamp does not say
- It does not say the pallet is Grade A, B or C; see grades
- It does not say the pallet is dry. Heat-treated pallets loaded into a trailer while still hot can grow mould, as the mould guide explains
- It does not say the pallet is new; used pallets can be re-treated
- It cannot be added by a seller who is not an approved treater
Do you need one?
Pallets that cross a border by sea or air in most cases do. A domestic load does not. For the nearest border, read shipping pallets to Canada, and for stock bought with the stamp, see heat-treated pallets.
Reading a real stamp, left to right
Look for the wheat-ear symbol of the International Plant Protection Convention. Beside it sit the two-letter country code and the producer number. The treatment code, HT, comes last or beneath, and DB may sit alongside it. A mark with all of these is complete; a mark with the symbol and no code is not.
Why a stamp can be wrong
- The stamp is smudged and cannot be read at the border
- The treater's number is missing or belongs to another facility
- Parts of the pallet have been replaced with untreated boards
- The pallet was repaired after treatment
A repaired pallet is the usual trouble. Replace one board with an untreated one and the pallet no longer meets the standard, even though the old stamp is still on the stringer. That is why export shippers often buy new stock for each shipment.
Buying pallets for export
Check the stamp before the pallet is loaded. A pallet without a legible mark can be refused at the port. If any pallet in a lot is marked wrongly, set it aside and replace it.
Where the mark sits
The mark is normally applied to two opposite faces of a pallet, on the stringers or the blocks, where it is easy to see. A pallet with a mark on only one face may be questioned.
Reading the mark
The mark on a heat-treated pallet shows the ISPM 15 symbol, a country code, a producer code and the letters HT. An inspector at a border or a receiving dock looks for these, and a pallet with a missing or smudged mark may be refused.
The mark is applied by an approved producer. A repair done afterwards with untreated lumber can void it, so ask whether any repairs were made from heat-treated wood.
Source: Wikipedia, "ISPM 15" (read 10 November 2026). Last reviewed 12 November 2026.
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Last reviewed 12 November 2026.