Ablative armor is armor designed to negate damage by itself being damaged or destroyed through the process of ablation. In contemporary spacecraft, ablative plating is most frequently seen as an ablative heat shield for a vehicle that must enter atmosphere from orbit. In a military application, ablative armor would undergo a state change on weapon impact, perhaps vaporising, or disintegrating to a fine powder. This state change would carry energy away from the armored vehicle and into the vaporized armor material. In addition, the expanding layer of ablated vapor would physically push additional hot gas away from the shield in a process known as blowing.
Ablative armor is distinct from the concept of reactive armor, which uses a sandwich layer of explosives to disrupt the thrust of armor piercing ammunition, and is actually in common use in modern armored vehicles.