An apocalyptic substance mentioned in Kurt Vonnegut, Jr.'s novel Cat's Cradle. In the novel, ice nine was created by Felix Hoenikker, who was interested in a form of ice that was stable at room temperature and standard pressure. Unfortunately, it could also create a chain reaction that would solidify all water, including the oceans and thus destroy all life on Earth.

Vonnegut was a dropout from Cornell University, and had studied Chemistry and was familiar with various phases of ice. Garden variety ice, the kind you see in snowflakes, is called ice-one and has a familiar hexagon arrangement. Under different conditions, different arrangements can occur. Ice-nine has not yet been created in a lab, as it requires incredible pressures. However, scientists have discovered up to ice-eleven and ice-twelve.