What type of material is used to insulate while also being noncombustible?

Gypsum is the correct choice because it is known for its properties as a noncombustible material that also provides effective insulation. Gypsum board, commonly used in construction, helps to slow the spread of fire and can protect structural elements from heat, thereby enhancing safety in building design. Its effectiveness as a fire-resistant material comes from its ability to prevent fire from penetrating walls and ceilings, offering a barrier that can withstand high temperatures.

Wood, while a good insulator, is combustible and can ignite easily, making it unsuitable for fireproofing applications. Steel, although noncombustible, does not provide insulation value on its own; it requires additional materials to achieve that function. Zinc is primarily used in coatings and has its own properties, but it is not used as an insulating material. Thus, gypsum stands out as the material that meets both criteria of being noncombustible and providing insulation.