What material is commonly used to insulate the outer surface of a boiler from heat?

Refractory material is commonly used to insulate the outer surface of a boiler from heat because it possesses high-temperature resistance and is capable of withstanding extreme conditions without losing its structural integrity. Refractory materials are designed to reflect heat and protect surrounding structures and personnel from high temperatures generated within the boiler. This type of insulation is crucial for maintaining safety and efficiency in boiler operation, as it minimizes heat loss and helps maintain optimal temperature levels within the system.

In contrast, steel is primarily used for the structural components of the boiler itself rather than insulation, as it can conduct heat rather than resist it. Wood and plastic are generally not suitable for use in high-temperature settings such as a boiler due to their combustibility and tendency to degrade when exposed to heat, which makes them impractical as effective insulative materials in this context.