2TheApex: 65% Zinc Oxide; 20% Gutta-Percha; 10% metal sulfites; 5% waxes and resins (Friedman)It's mostly Zinc Oxide. We call it Gutta-Percha since that is what gives it unique properties we enjoy, like plasticity. The material was used as an obturation material over 100 years ago. It comes from the sap of a tree that grows in Malaysia. It is also safe to use in patients that are allergic to latex. (American Latex Allergy Association) Gutta-percha has stood the test of time and it still the standard by which all obturation materials are judged.