Answer is: polystyrene.
Expanded polystyrene is used to manufacture foam cups.
Polystyrene production is several million tonnes per year.
Polystyrene is a synthetic aromatic hydrocarbon polymer made from the monomer styrene.
Styrene (ethenylbenzene) is an organic compound with the chemical formula C₆H₅CH=CH₂. It is a colorless oily liquid.