Clay brick is a refractory product with Al₂O₃ content of 30-48%, made using clay clinker as aggregate and refractory clay as binder. The raw material for clay bricks is clay minerals. Refractory clay can generally be divided into soft clay and hard clay. In the manufacturing process, the former has good plasticity after adding water and sinters easily, mostly used as a binder; the latter is mostly calcined and used as clinker.

Clay bricks are weakly acidic refractory bricks that become stronger with increasing SiO₂ content, and are therefore commonly used as lining materials for acidic furnaces. Based on bulk density, they are further classified into ordinary clay bricks, low porosity clay bricks, and low creep clay bricks. By application, clay bricks can be roughly divided into: coke oven clay bricks, blast furnace clay bricks, hot blast stove clay bricks, glass kiln clay bricks, cement kiln large clay bricks, and carbon baking furnace clay bricks.