CN code 390791 covers other unsaturated polyesters in primary forms. Unsaturated polyester resins (UP, UPR) are prepolymers containing unsaturated bonds (usually from maleic anhydride or fumaric acid) that can be cross-linked using styrene or other reactive monomers. Uncured UP resins are liquids or pastes that, upon addition of initiator (peroxide) and accelerator, cure into a cross-linked polymer with excellent mechanical properties. UP resins are the primary matrices for glass fibre reinforced composites (GRP/FRP) used in construction, automotive, boats, tanks and industrial installations. Products come as liquid resins, most commonly in styrene solution.

Importing unsaturated polyester resins into the EU is subject to REACH. Styrene contained in UP resins is a REACH-registered substance with CLP classification as potentially damaging to hearing organs. Residual maleic anhydride is an irritant. UP resins in styrene solution require SDS addressing styrene hazards including inhalation exposure. The VOC Directive limits styrene emissions during lamination. UP resins for food contact (e.g. drinking water tanks) must comply with relevant national and EU water and food contact material regulations. Transport of UP resins in styrene solution is subject to ADR Class 3.

When importing UP resins under CN code 390791, customs documentation should include a specification with resin type (orthophthalic, isophthalic, vinyl ester), styrene content, viscosity, reactivity and commercial form. Duty rates should be verified in the TARIC system. Major UP resin producers include Polynt-Reichhold, Scott Bader, AOC Aliancys, BASF and Chinese manufacturers. The UP resin market exceeds 10 million tonnes annually. Transport is in drums or IBC containers as ADR Class 3 dangerous goods.