Electro Reactive Plating, or E-Plates, is a type of armor used by certain Vaul units composed of Plasteel alloys and electro reactive polymers.
When subjected to high levels of electricity, the molecular structure of the alloy polarizes and enters Transphase where density and durability is increased significantly (Star Trek - Enterprise: Polarized hull plating). The appearance of the alloy also changes from black or dark grey to pure white (Halo: TR Steel).
While not as effective as Plasma Shielding, E-Plating is resilient to small caliber projectiles and the primitive attacks of weak Zerg strains (Gundam SEED: Phase Shift armor). Unfortunately, the plating requires high levels of energy from most primary systems. This and the tremendous increase in density renders users immobile until the plates are deactivated (Mutant X: Jesse Kilmartin).