Paraformaldehyde is a solid with a much lower vapor pressure than formalin (37–50% aqueous formaldehyde), reducing inhalation exposure risk during transport and storage. It still requires DOT hazardous materials labeling as a flammable solid and an irritant, but its solid form simplifies packaging, reduces leakage risk, and can lower freight costs for international shipments compared to bulk liquid formalin.

Because this heading is an NES (not elsewhere specified) provision, importers must confirm that the compound is not more specifically described under a named aldehyde heading or under ketone, acid, or ester headings that may capture bifunctional molecules. Providing the full IUPAC name, CAS number, and a structural diagram to the customs broker — along with any relevant CBP binding rulings — is the most reliable way to defend the classification.