PET HS Code 3907.61 or 3907.69: Declaring Viscosity Correctly

Polyethylene terephthalate (PET) is a thermoplastic polyester obtained by melt-phase polycondensation of purified terephthalic acid (PTA) or dimethyl terephthalate (DMT) with monoethylene glycol (MEG). Although the name contains “polyethylene,” PET is not a polyolefin; it is a polyester, and heading 3901 does not apply. In primary forms—liquids, pastes, powders, granules, pellets, and flakes—PET is classified in heading 3907 of the Harmonized System. The border between subheading 3907.61 and subheading 3907.69 is not controlled by molecular weight, melt flow index, crystallinity, food-contact status, or intended downstream use. It is controlled exclusively by viscosity number. Subheading 3907.61 covers polyethylene terephthalate having a viscosity number of 78 ml/g or higher. Subheading 3907.69 is the residual position for PET below that threshold. A customs declaration under 3907.61 or 3907.69 therefore requires a method-specific viscosity number, not an unqualified “IV” value.

The legal threshold of 78 ml/g is dimensionally equivalent to 0.78 dL/g, but the Harmonized System criterion is viscosity number. Viscosity number is defined in ISO 1628-1 as specific viscosity divided by concentration: (ηrel − 1)/c. Many commercial documents instead report inherent viscosity per ASTM D4603-18, defined as ln ηrel / c. The two parameters are not interchangeable. At a test concentration of 0.5 g/dL, a resin with a viscosity number of 78 ml/g has a calculated inherent viscosity of approximately 0.66 dL/g when solvent and temperature effects are ignored. Therefore, a Certificate of Analysis that reports “IV 0.66” cannot be read as proof that the resin falls below 3907.61 unless the method and calculation basis are identified.

What Distinguishes HS 3907.61 from HS 3907.69 in a Binding Tariff Classification?

The wording of subheading 3907.61 is “poly(ethylene terephthalate), having a viscosity number of 78 ml/g or higher.” Subheading 3907.69 covers other polyethylene terephthalate. The viscosity number is measured on the material in the condition in which it is traded. End use is not determinative. A melt-phase PET chip of 64 ml/g imported for later solid-state polymerization remains classified under 3907.69, even if the buyer intends to convert it to 82 ml/g bottle resin. A post-consumer recycled PET pellet with viscosity number of 79 ml/g is classified under 3907.61; if thermal and hydrolytic degradation during extrusion has reduced the same material to 74 ml/g, it falls under 3907.69. PET waste, parings, and scrap are excluded from heading 3907 and generally fall in heading 3915, so recovered flake traded as scrap cannot be classified by viscosity alone.

The primary-form rule is set out in Note 6 to Chapter 39 of the Harmonized System. Liquids, pastes, powders, granules, pellets, and flakes are all primary forms. The viscosity threshold applies across those forms, but sampling and sample preparation can influence the measured value. Customs laboratories typically base a viscosity determination on dry, representative resin rather than on material contaminated with label adhesive, cap liner residues, or film fragments. Food-contact clearance under 21 CFR 177.1630 or REACH registration does not alter the tariff subheading. A food-grade PET resin measured at 74 ml/g remains 3907.69; a non-food technical resin measured at 81 ml/g is 3907.61.

In the World Customs Organization Explanatory Notes to heading 39.07, the viscosity-number criterion is applied in conjunction with the primary-form rule of Chapter 39 Note 6. The notes do not prescribe a single test method for every national administration, but ISO 1628-5:1998 is the method most commonly cited by national rulings because it reports viscosity number directly in millilitres per gram. Where a national customs laboratory uses ASTM D4603-18, the entry should carry a supplementary ISO value or a documented conversion curve. The burden of proof lies with the declarant to show that the product was correctly classified at the time of importation.

The commercial ranges in the following table are indicative because viscosity number distribution varies with catalyst system, comonomer content, and finishing technology. The only legal boundary is 78 ml/g.

During solid-state polymerization, amorphous melt-phase PET chips are first crystallized at 150–170 °C and then held at 200–220 °C under vacuum or dry nitrogen to remove ethylene glycol and acetaldehyde and to extend chain length. Continuous solid-state polymerization units operating at vacuum levels of 1–10 mbar and residence times of 8–16 h raise viscosity number from 60–65 ml/g to 80–85 ml/g for bottle resin. The final value is sensitive to crystallizer outlet moisture, diethylene glycol content, catalyst residues, and gas flow distribution. Near the tariff boundary, batch-to-batch variation can move a target of 79 ml/g by 1–2 ml/g. If a lot declared as 3907.61 is tested by customs at 77.4 ml/g, reclassification to 3907.69 can follow with retroactive duty adjustment. Exporters of threshold-sensitive resin should set an internal release target no lower than 80 ml/g, or segregate and document lots with a defined viscosity-number distribution.

In melt-phase PET finishing, viscosity number is limited by thermal degradation and agitator torque; typical melt-phase output is 55–65 ml/g. To exceed 78 ml/g, producers use solid-state polymerization or liquid-state finishing after melt-phase prepolymer. The transition from 3907.69 to 3907.61 therefore frequently occurs inside the same physical supply chain: a low-viscosity melt-phase chip is exported for toll solid-state polymerization, and the imported product after polymerization is a different HS subheading despite a similar chemical structure.

Mechanical recycling creates the same boundary condition. Washed and extruded post-consumer bottle flake can enter the range 70–76 ml/g after thermal and hydrolytic degradation during extrusion. If the flake or pellet is traded as a primary form and tested below 78 ml/g, it is 3907.69. If it is traded as waste or scrap, classification may shift to heading 3915. The distinction depends on the commercial specification and whether the material remains in primary form.

If ASTM D4603-18 Reports Inherent Viscosity Instead of ISO 1628-5 Viscosity Number

Customs entries in the Americas frequently depend on ASTM D4603-18 because resin suppliers report PET inherent viscosity in dL/g. The ASTM method uses a 60/40 w/w phenol/1,1,2,2-tetrachloroethane solvent at 30 °C and calculates inherent viscosity as ln ηrel / c. The ISO method for PET viscosity number, ISO 1628-5:1998, uses a 50/50 w/w phenol/1,2-dichlorobenzene solvent at 25 °C and calculates viscosity number as (ηrel − 1)/c. The test concentration is commonly 0.5 g/dL in both procedures. The numerical gap between the two parameters is not constant and can exceed 10 ml/g at relative viscosities typical of bottle-grade PET. Solvent and temperature differences further shift the measured value. A declaration based on ASTM inherent viscosity therefore cannot be substituted for an ISO viscosity number without a separate measurement or a documented correlation curve.

A CoA that states only “IV 0.78 dL/g” is ambiguous for tariff purposes. If the value is viscosity number under ISO 1628-5:1998, the resin qualifies for 3907.61. If the value is inherent viscosity under ASTM D4603-18, the resin may have a viscosity number substantially above 78 ml/g. However, the legal entry requires a value expressed against the HS criterion. The correct declaration under 3907.61 should either report “Viscosity number per ISO 1628-5:1998: 81 ml/g” or state the ASTM inherent viscosity with the method, solvent, temperature, and a conversion note that permits a customs chemist to verify the threshold.

Measurement under ISO 1628-5:1998 is carried out in a suspended-level Ubbelohde capillary viscometer with temperature control better than ±0.05 °C. The PET sample is dissolved in the phenol/1,2-dichlorobenzene solvent at 90–100 °C, filtered, and equilibrated in the bath. Incomplete dissolution, moisture ingress, or solvent oxidation raises flow-time scatter and can push a borderline lot below the legal threshold. Viscosity declarations should be supported by duplicate or triplicate runs and retention of raw flow times.

Certificate of Analysis Data Fields for Viscosity-Declared PET Shipments

A customs-ready CoA for PET should separate product name, HS subheading, viscosity parameter, method, solvent, temperature, and calculation basis. The product name should identify the material as poly(ethylene terephthalate) in primary form. The HS subheading should be selected from the measured viscosity number at importation. The viscosity parameter should be “viscosity number” in ml/g, not “intrinsic viscosity” or “inherent viscosity” unless the method is explicitly identified. The test method should be ISO 1628-5:1998 for direct HS compliance or ASTM D4603-18 with a clear conversion note. The solvent and test temperature should be recorded because both affect the measured value.

The CoA should not report melt flow index as a substitute for viscosity number. PET melt flow index is insensitive to the chain-length differences that control the HS threshold and is not a recognized tariff parameter under 3907.61 or 3907.69. Pellet size, crystallinity, and bottle preform performance data also do not determine classification.

Customs laboratory verification of a 3907.61 entry follows the method stated on the declaration or a nationally accepted equivalent. A representative sample is dissolved, filtered, and measured in a capillary viscometer. If the re-measured viscosity number falls below 78 ml/g, the entry may be reclassified under 3907.69 regardless of the exporter’s declared grade. Borderline lots between 76 ml/g and 80 ml/g are the most dispute-prone because solvent purity, sample moisture, dissolution time, and viscometer calibration each contribute to the result. Importers and exporters should retain raw viscometer flow times, solvent lot data, and calibration records against certified viscosity reference oils.

The operational boundary is narrow. A PET primary form is declared under 3907.61 only when the measured viscosity number, determined by ISO 1628-5:1998 or a documented and converted method, is equal to or greater than 78 ml/g. If the measured value is below that threshold, the correct subheading is 3907.69, and the declaration should state the method used to obtain the viscosity value.