Dicyclopentadiene or DCPD is the dimer of cyclopentadiene (CPD) formed by a Diels-Alder addition reaction. DCPD products originate from high-temperature cracking of petroleum fractions and are best characterized as highly reactive intermediates used for a wide range of resins, i. e. aromatic hydrocarbons, unsaturated polyesters, phenolics and epoxies.Dicyclopentadiene is a man-made substance produced by heating crude oil products. It's a colourless, waxy, flammable solid or liquid, with a camphor-like odour. As dicyclopentadiene enters the air, it breaks down quickly into simpler, less-toxic chemicals. However, it can stay unchanged for a long time in soil and in water. DCPD is not a common ingredient of products used in homes. It is used to make bug sprays, paints, and varnishes. Most dicyclopentadiene in the environment results from industrial processes and from improper waste disposal.