Neutroniumbased
Neutroniumbased is a theoretical substance that, if it exists, would be composed primarily of neutronium. Neutronium is a hypothetical form of matter composed almost entirely of neutrons, believed to exist in the cores of neutron stars. The extreme gravitational pressure within a neutron star is thought to overcome the electrostatic repulsion between protons and electrons, forcing them to combine into neutrons.
If neutronium could be formed or found in a stable, macroscopic form, it would be incredibly dense.
The concept of neutroniumbased matter is largely speculative and primarily arises in theoretical physics and science