Which of the following is a type of insulation used inside furnaces?

• A. Fiberglass
• B. Ceramic wool
• C. Fire Brick
• D. Vermiculite

Answer: (C)

Furnace interiors must be lined with materials that can withstand direct flame and very high temperatures without breaking down. Fire brick is a refractory brick used as the interior lining of furnaces and kilns. Its composition lets it resist heat, endure thermal shocks, and hold up under repeated heating and cooling, all while protecting the steel shell and helping retain heat inside the chamber. That sturdy, heat-tolerant lining is why it’s used inside furnaces. While fiberglass and ceramic wool are excellent insulators in many applications, they aren’t typically used as the primary interior lining because they don’t offer the same combination of heat resistance and structural durability. Vermiculite serves as insulation in some setups but doesn’t form the solid interior lining that fire brick provides.