Polarized hull plating was a defensive technology that was technologically inferior shields. In a battle situation, electromagnetic power could be applied to the hull materials, making them several orders of magnitude harder. This technology was used on starships such as the Template:ShipClass in the 22nd century, before Starfleet had developed shielding capabilities. During the months the Enterprise was in the Delphic Expanse, polarization technology on Earth had been improved by 12%. (Star Trek: Enterprise; ENT: "Home")
In 24th century, starships occasionally polarized their hull plating though not typically as a defensive countermeasure against enemy weaponry. One example was disrupting an enemy's tractor beam by rotating the frequency of the hull plating's electromagnetic field. Ships also sometimes polarized their hull plating to help mask their sensory signature, which worked by interfering with the enemy's sensors. (DS9: "In Purgatory's Shadow"; VOY: "Equinox, Part II").