Insulating fire bricks are a type of refractory fire brick utilised in the construction of insulation for ovens and kilns. The bricks soft and light weight, and may be cut by a handheld hack saw, with a masonry chisel or drill bit. The bricks are generally of a light brown to white colour due to the clay materials that they are made from. Insulation in general is commonly performed by the creation of air pockets in the insulating medium. For this reason as with fire blanket and vermiculite cement, insulating fire bricks create the insulating effect by containing multiple small spaces for air to reside. As with standard dense fire bricks, insulating fire bricks are made from similar fire clay and can withstand very high temperatures. These bricks however do not have good heat retention properties and so cannot function in the same role as regular fire bricks. If they were to be placed within the oven as the hearth or vault wall the oven would not function adequately. The heat generated by the fire would not be absorbed nor radiated back into the oven.
Insulation bricks are commonly used in the construction of personal kilns or industrial ovens, and less so with wood fired pizza ovens. Generally these ovens are heated via electrical elements or gas burners rather than traditional wood fires. During construction the bricks may be implemented as either the initial insulating lay on the outside of the inner oven vault, or as further secondary insulation. Insulating fire bricks have low thermal conductivity and don't conduct heat as with regular fire bricks. For this reason they are a great form of initial insulation which may come into contact with high temperatures. The insulating bricks may be placed directly on the outside of the inner oven wall of fire bricks, and thus create a barrier to minimise the heat escaping through to the outside environment. The thinker this level of insulation the better the oven will perform efficiently and be able to maintain useable temperatures for a period of time.
As with dense fire bricks, insulating fire bricks are generally purchased from brick or refractory suppliers. Individual bricks with dimensions of 76mm x 230mm x 110mm) cost around $4 each.