A firebrick is a special brick that can sit in very strong heat without cracking or melting. People use them to line chimneys, fireplaces, wood stoves, pizza ovens, and the inside of kilns and factory furnaces — anywhere ordinary bricks would break. They are made of clay that stands up to fire. They often look a little paler than the red bricks of a house wall. You would not build a whole house from firebricks; they are for the hot parts. The name is simply a brick for fire — not a brick that is on fire.