Ablative Armor

From: Star Trek: Deep Space Nine

Caption: U.S.S. Defiant

Star Trek: Voyager

Episode: VOY 181 - Message in a Bottle

An outer hull layer on some Federation starships that is designed to vaporize under weapons fire, thereby dissipating energy and protecting the ship's interior.

The prototype ships U.S.S. Defiant and U.S.S. Prometheus were equipped with ablative armor.