A substance that has yet to be created on earth. But if it would exist it should be designated as number 115 in the periodic table. According to Robert Lazar, it's the substance he came in contact with when he was working at the Area-51. It's used in some way with the propulsion engine in the crafts to create anti-gravity.

Lazar claims that when element 115 is modified in a certain combination of protons, neutrons, and electrons, it will produce a stable form of itself. This new stable combination releases a larger, more powerful gravitational field than other elements. This force that is produced from the element 115 is not like that which holds us to the earth and the planets in orbit. The element produces a field of the same kind that holds atoms together. This gravitational field bends the space-time continuum and travels in a non-linear direction. It's like that the craft is standing still with the space moving against it.