Plastic-X is green in color and has been described as "living plastic", possessing a cellular structure. The substance can be molded into any shape and cannot be harmed by any conventional means. While Plastic-X can be melted down, its properties do not change with its change in state.
Plastic-X is what gives the Plax, who are all made of this substance, their shapeshifting and nearly invulnerable bodies. Their hive-mind is such in tune with the Plastic-X that several Plax can reform themselves even after having all their cells mixed into one mass.