Sealing ring for Bialetti 18-cup Moka Express in beige. Number of cups: 18. Outer diameter of the seal: 9 cm, inner diameter of the seal: 7 cm. Made from natural rubber, a rubber product produced without petroleum. Natural rubber is primarily obtained by tapping the bark of the rubber tree. The resulting plant sap, also known as latex, is collected and acidified with acetic acid. Natural rubber is characterized by high elasticity and durability, is water-resistant, and is sustainably cultivated in mixed cultures.