Cyclopentadiene is a manmade chemical. It's either a clear liquid or solid, with a sweet odor like turpentine or camphor.
Manufacturers use cyclopentadiene to make resins and other chemicals.
Cyclopentadiene is not commonly found in home-use products. It is found in tobacco smoke and car exhaust. It's also found in exhaust from coal and oil-fueled fires. When released into the air, cyclopentadiene breaks down to a less toxic chemical within a few hours. If a home water supply is contaminated, people could inhale the chemical when they cook, do laundry, or bathe.