Ablative armor is a type of protective hull plating used aboard starships designed to disintegrate at a controlled rate under enemy fire. It dissipated the effects of directed energy weapons, decreasing damage to the main hull of the ship and thereby providing an extra layer of defense. Starfleet first began using ablative armor technology aboard Defiant-class starships in the early 2370s.
It should be noted that under certain conditions, chroniton particles generated by Romulan cloaking devices can become lodged in the ablative armor matrix. On at least one occasion, a temporal surge caused by the explosion of a microscopic singularity shifted the chroniton particles in the hull into a high state of temporal polarization, thus causing a transporter beam to be redirected through time.