The heat-insulating refractory is made from fire-resistant lightweight aggregate and powdered material, binder and admixture. It is generally stipulated that the volume density is less than 1800kg/m3, or the total porosity is more than 45%. This kind of castables is small in volume density and has good heat insulation performance, also known as lightweight refractory castables. It is widely used in insulating layer for kiln and thermal equipment in metallurgical, petrochemical, electric power and building materials industries, and also for its working layer or load-bearing component.

There are many varieties of heat insulating refractory castable, which are generally classified according to the method of making light aggregate, the type and the performance of the binder. The most commonly used are light refractories, porous clinker, hollow ball, ceramsite and expanded perlite, vermiculite and so on. Heat insulated castables - like composition and performance are shown in table 3-145. The binder mainly contains aluminate cement, Portland cement and so on, and its dosage is 15%~40%. Sometimes, phosphoric acid, aluminum phosphate and water glass are also used as binder. Its additives mainly include expander and water reducing agent. The effect of expansion agent is to counteract partial contraction at high temperature and enhance its volume stability.