Hexabromocyclododecane (HBCD or HBCDD) is a brominated flame retardant. It consists of twelve carbon, eighteen hydrogen, and six bromine atoms tied to the ring. Its primary application is in extruded (XPS) and expanded (EPS) polystyrene foam that is used as thermal insulation in the building industry.

HBCD's toxicity and its harm to the environment are currently discussed.European Chemicals Agency decided to include HBCD in the SVHC list[3], Substances of Very High Concern, within the REACH framework. HBCD has been found widely present in biological samples from remote areas and supporting evidences for its classification as Persistent, Bioaccumulative and Toxic (PBT) and undergoes long-range environmental transportation.

Due to its persistence, toxicity, and ecotoxicity, a global ban on HBCD is currently being considered under the framework of the Stockholm Convention on Persistent Organic Pollutants.[6] HBCD is also included on the list of substances added to a proposal to revise the RoHS (Restriction of Hazardous Substances) directive.[7] There is a large and increasing stock of HBCD in the anthroposphere, mainly in EPS and XPS insulation boards.[8]