EPDM o-rings, or ethylene propylene o-rings, are a family of synthetic elastomers with lower cost steam and chemical resistance, particularly for applications involving solvents, acids and other mild chemicals. EPDM can be cured with either Sulphur or Peroxide. Sulphur curing is less expensive and easier to process but the product may be tacky and can exhibit some bloom. Peroxide curing is more difficult to process but provides better chemical, thermal, and aging resistance.