A fire brick, firebrick, fireclay brick, or refractory brick is a block of ceramic material used in lining furnaces, kilns, fireboxes, and fireplaces. A refractory brick is built primarily to withstand high temperature, but will also usually have a low thermal conductivity for greater energy efficiency. Firebricks are ceramic bricks designed for high-temperature uses, such as within furnaces or kilns. They come in two standard sizes, either 229 x 114 x 76mm or 229 x 114 x 64mm. Another option for fire bricks is split bricks which will be half the standard thickness, at 229 x 114 x 32mm.