Hard armor is a term that is used for very strong and thick materials used in military for protection. There are two kinds of armor. One is the blast-proof armor which has no defects while the other kind is the dust-proof armor. Blast-proof armor is a special case, because it has no weakness. It can be used even when it is not in use.
For hard armor, if you have a bomb that explodes near you, you can protect yourself by covering your head with a hard helmet. If you have a direct hit from an anti-tank or anti-aircraft gun, you can cover your head with hard helmets. Hard armor can also be used to shield other materials like vehicles, boats, planes, motor boats, ships, tankers, etc. because it has the ability to reduce any damage caused by the explosion, fire, blast, rocks, bullets, and other projectiles.
Another important function of this armor is that it helps to divert the energy of an impact or energy loss into something else. It can stop an explosion from blowing up an aircraft. It can absorb energy to deflect a bullet or other projectile. It can also absorb the shock wave of an explosion. This armor is used in aircraft, military helicopters, tanks, aircraft, etc.