Considering the world of commercial transparent polymers, Daikyo Crystal Zenith® cyclic olefin polymer (COP) clearly stands out – having very good resistance to oxygen/water and compatibility with drug product (it comprises only carbon and hydrogen). Other transparent polymers may suffer limitations, in one or more ways. For example, poly(vinylidene chloride) has outstanding resistance to oxygen/water, but lacks compatibility; sterilization can result in release of HCl. For parenteral drug products, polymer-based containment/delivery systems have many advantages compared to glass.