HTSUS classification walkthrough: a two-part epoxy adhesive kit (Section VI, GRI 3(b))

Chemical-family classification questions on the exam reward knowing that “chemicals” is not one chapter, it is Section VI, Chapters 28 to 38, organized by chemical function rather than by a single unifying rule. Adhesives are a clean, frequently-tested example inside that Section. See the machinery walkthrough for the first worked GRI 3(b) set example and the plastics walkthrough for how a neighboring Section handles material-versus-function questions. The GRI guide covers the rule order, and the glossary defines HTSUS and tariff classification.

Step 1: find the Section and Chapter

The good is a two-part epoxy adhesive, sold at retail as a kit: a tube of resin and a tube of hardener, packaged together, meant to be mixed in equal parts immediately before use. Chemical products of the “allied industries” sit in Section VI, Chapters 28 to 38. Within Section VI, glues and adhesives are not grouped with the general organic or inorganic chemical chapters (29 and 28); they have their own dedicated chapter. Chapter 35, “Albuminoidal substances; modified starches; glues; enzymes,” is where prepared adhesives live, a fact that surprises candidates who default to Chapter 38, “Miscellaneous chemical products,” for anything that does not obviously belong elsewhere in Section VI.

Step 2: find the heading under GRI 1

Heading 3506 reads: “Prepared glues and other prepared adhesives, not elsewhere specified or included; products suitable for use as glues or adhesives, put up for retail sale as glues or adhesives, not exceeding a net weight of 1 kg.” That heading text is written specifically to capture retail-packaged adhesive products, which is exactly our kit, so GRI 1 places the good in 3506 directly.

Step 3: find the subheading

Heading 3506 splits first by retail packaging and weight, then by chemical basis:

Subheading	Description
3506.10	Products suitable for use as glues or adhesives, put up for retail sale not exceeding 1 kg net weight
3506.91	Adhesives based on polymers of headings 3901 to 3913 or on rubber
3506.99	Other

A small retail epoxy kit, under 1 kg net weight and sold as a glue or adhesive product, falls under 3506.10, at the rate line 3506.10.50.00 for a product other than animal or casein glue. If the same epoxy adhesive were instead imported in bulk (a 25 kg drum for industrial use, not put up for retail sale), the 1 kg retail-packaging test in 3506.10 would no longer be met, and the classification would move to 3506.91 or 3506.99 depending on the adhesive’s chemical basis, an epoxy resin system generally falling to 3506.91 as a polymer-based adhesive of the kind covered by headings 3901 to 3913. Packaging and quantity, not just chemistry, decide the subheading here.

Step 4: why the two-part kit is one classification, not two

A two-part epoxy is, strictly, two separate chemical preparations, resin and hardener, that only become an adhesive when combined. A candidate could be tempted to classify the resin under one heading (an epoxide resin of Chapter 39, heading 3907) and the hardener under another (a chemical of Chapter 38 or 29). That is the wrong frame for how the kit is imported and sold. Put up together, in the fixed proportion needed for their joint use, for retail sale as a single adhesive product, this is the same “goods put up in sets for retail sale” pattern as the drill kit in the machinery walkthrough: GRI 3(b) treats it as a unit, classified according to the component that gives it essential character. Here that is straightforward, because the resin and hardener have no independent retail purpose apart from being mixed to form the adhesive; the adhesive function itself is the essential character, which is exactly what heading 3506 already describes, so the heading-level and GRI 3(b) analyses agree and land on the same answer.

Why this is not a Section VI mixture question

Section VI also has its own legal note dealing with mixtures of chemicals, aimed at cases like combining two organic compounds into a new preparation not separately named anywhere in Chapters 28 to 38, which get classified as if they were a product of the heading that most specifically describes them, or failing that, the heading appropriate to the chemical that characterizes the mixture. That note matters for genuinely blended chemical products. It is not the controlling analysis here, because heading 3506 already names our exact product, “prepared glues,” directly, so GRI 1 resolves the heading before any mixture-note analysis is needed; the only remaining question is the retail-set treatment of the two components, which GRI 3(b) answers.

Practicing this pattern

Chemical questions reward knowing which chapter inside Section VI actually houses a given product function (dyes in 32, soaps and surfactants in 34, glues in 35, explosives in 36, photographic chemicals in 37, everything else in 38) rather than defaulting to Chapter 38 for anything unfamiliar. Drill the chapter map in the chapter locator, sequence the rules in the GRI order drill, and test the pattern against original questions in the free practice test.

Sources: Chapter 35 and Section VI titles verified against the hts.usitc.gov chapter index; heading 3506 text and subheading structure (3506.10, 3506.91) verified against the U.S. International Trade Commission's Harmonized Tariff Schedule search and export tools at hts.usitc.gov, both checked 2026-07-29. GRI 3(b) and the "goods put up in sets for retail sale" concept are stated in the General Rules of Interpretation published at hts.usitc.gov. This is a plain-English walkthrough; the official HTSUS text and current Section VI notes govern, so confirm the exact text and any applicable CBP ruling before relying on it for an actual entry.