Heat Treated Stamp: ISPM 15 Rules and Port Enforcement

The heat-treated stamp is the ISPM 15 mark burned or printed onto wood pallets, crates, and other shipping wood to certify the material was heated enough to kill insects and larvae inside it. The standard behind the mark comes from the International Plant Protection Convention (IPPC), and in the United States it is enforced through federal regulation. Solid wood packaging arriving at a U.S. port without a valid mark is refused entry and sent back at the importer’s expense.¹

What a Valid Stamp Must Show

The mark has a fixed format. Every compliant stamp contains four elements:

The IPPC logo, a stylized plant symbol next to the letters “IPPC.”
A two-letter ISO country code identifying where the wood was produced and treated (for example, “US”).
A unique number identifying the specific facility that performed the treatment.
A treatment code: “HT” for conventional heat treatment, “DH” for dielectric heating such as microwave, or “MB” for methyl bromide fumigation.¹

The facility number is what makes the system traceable: if a pest surfaces in a shipment, regulators can follow the number back to the treater. The stamp must be legible and permanent, applied with a branding iron, ink stamp, or stencil directly on the wood. Hand-drawing is not allowed, and federal rules require the mark to appear in a visible location on each piece, preferably on two opposite sides.¹

IPPC guidance recommends avoiding red or orange ink, because those colors are associated with hazardous materials labeling. It’s a recommendation rather than a prohibition, but most facilities stay with black.²

Which Wood Packaging Needs the Stamp

ISPM 15 applies broadly to solid wood used to support, protect, or move cargo across borders. That covers pallets, crates, packing blocks, load boards, pallet collars, skids, drums, cases, and dunnage (the loose lumber used to brace cargo inside a container).² If it is raw or semi-processed wood and it travels with an international shipment, it almost certainly needs the mark.

Materials That Are Exempt

Some wood materials are processed enough that pest risk is already gone, and they fall outside the stamp requirement:

Engineered wood products such as plywood, oriented strand board, and particleboard, made with glue, heat, and pressure.
Presswood pallets made from compression-molded wood chips.
Any wood 6 mm or less in thickness.
Wine and spirit barrels, if they were heated during manufacture.
Sawdust, wood shavings, and wood wool.
Wood permanently attached to freight vehicles or shipping containers.³

Plastic pallets carry no pest risk and sit outside the standard entirely.

What “HT” Actually Means

The “HT” code certifies that the wood was heated in a kiln or steam chamber until its core reached at least 56 °C (about 133 °F) and held that temperature for a minimum of 30 continuous minutes. The rule targets the core because pest larvae burrow deep into the grain, and surface heat is not enough.⁴

The other two treatment codes work differently. “DH” (dielectric heating) uses microwave or radio-frequency energy to heat wood from the inside out. The temperature threshold is higher: at least 60 °C for one continuous minute throughout the entire piece, reached within 30 minutes of starting treatment. This method is limited to wood where the smallest dimension is 20 cm or less. “MB” indicates methyl bromide fumigation, which the IPPC actively discourages because it depletes the ozone layer. MB is also limited to wood with a smallest cross-section of 20 cm or less, and several importing countries refuse MB-treated packaging or add extra restrictions, so shippers relying on it should confirm acceptance at destination before loading.⁵

“Kiln Dried” Is Not the Same as Heat Treated

Lumber stamped “KD” has been dried in a controlled environment to bring its moisture content down, usually to between 16 and 19 percent. That makes it more stable, but it does not necessarily mean the core hit 56 °C for the required 30 minutes. A KD stamp on its own does not satisfy ISPM 15. Wood that has been both dried and heat-treated may carry a “KD-HT” marking, but only the presence of HT (or DH) inside the official IPPC-format stamp meets the international shipping requirement.⁶

Who Is Allowed to Apply the Stamp

A facility cannot just buy a branding iron and start marking pallets. In the United States, any producer or treatment provider has to enroll in a monitoring program run by an accredited third-party agency. The American Lumber Standard Committee (ALSC) oversees this system and currently recognizes 15 independent agencies that audit and certify treatment facilities.⁷

To earn and keep certification, a facility has to prove it consistently meets the temperature and time requirements and keep detailed records of every treatment cycle: start and end times, the heat chamber used, wood species and dimensions, temperature readings at control points, and evidence the minimum was met.⁸ That paper trail is what makes traceback possible. Facilities remain subject to ongoing audits, and an agency can suspend the right to use the stamp if protocols slip. Only wood that has actually been treated under the certified program can be marked; stamping untreated wood is fraud and grounds for losing certification.

Repaired and Remanufactured Packaging

Pallets and crates get damaged and rebuilt all the time, and ISPM 15 draws a clear line between repair and remanufacture. If a pallet gets one or two replacement boards but keeps most of its original treated components, the original stamp stays valid, provided the added wood has also been treated. When packaging is fully remanufactured, it counts as brand-new material: all original marks must be permanently removed, the packaging has to go through the full treatment cycle again, and a fresh stamp is applied before it re-enters international trade.²

What Happens at U.S. Ports Without a Valid Stamp

U.S. Customs and Border Protection and the USDA’s Animal and Plant Health Inspection Service jointly enforce ISPM 15 at the border. An inspector at the port of first arrival has authority to order the immediate re-export of any regulated wood packaging arriving without the required mark.¹

When non-compliant material is found, inspectors issue an Emergency Action Notification (EAN) identifying the violation and spelling out what has to happen next.⁶ Options are limited: re-export the wood, or have it destroyed under APHIS supervision. Safeguarding steps like tarping or knockdown fumigation may be permitted to contain immediate pest risk, but fumigation is not accepted as a cure for unmarked packaging in the U.S. The wood leaves the country or is destroyed.⁹

All of it happens at the importer’s cost. Between rerouting freight, storage, supervised destruction, and delay, a single non-compliant shipment can run into thousands of dollars, and the importer is expected to cooperate with a traceback investigation that identifies where the failure occurred. Missed EAN deadlines can trigger a claim for liquidated damages against the importer, carrier, or bonded custodian. One narrow carve-out: wood packaging used by the U.S. Department of Defense to ship nonregulated articles, including commercial shipments under a DOD contract, may enter without the ISPM 15 mark.¹

1
eCFR. 7 CFR 319.40-3 – General Permits; Articles That May Be Imported Without a Specific Permit
2
International Plant Protection Convention. Explanatory Document for ISPM 15
3
ISPM15.com. ISPM15 Exemptions
4
International Plant Protection Convention. Explanatory Document for ISPM 15 – Section: Annex I
5
International Plant Protection Convention. Regulation of Wood Packaging Material in International Trade – ISPM 15
6
Animal and Plant Health Inspection Service. Import ISPM 15-Compliant Wood Packaging Material Into the United States
7
American Lumber Standard Committee, Inc. WPM – Accredited Agency Lists
8
International Plant Protection Convention. Explanatory Document for ISPM 15 – Section: Verification
9
U.S. Customs and Border Protection. Import and Export Requirements for Wood Packaging Material Into the United States