Clay is the primary raw material used in the making of genuine brick, so what people generally refer to as "brick" is clay brick. Clay brick are manufactured using three basic methods, resulting in three basic types: extruded brick, machine-molded brick, and handmade brick. Extrusion is the most efficient and least costly of the three methods, so extruded brick are generally the least expensive to buy. Handmade brick are made by human hands filling individual molds, resulting in folds and other brick-face characteristics impossible to create any other way. Machine molded brick offer similar colors to handmade brick, but without the same unique character in the individual brick faces. Manufacturers of some other materials, such as concrete, use the term "brick" to describe some of their products, but genuine bricks are always made of clay.