Which type of insulation is most commonly used in exterior walls?

Fiberglass batts are the most commonly used type of insulation in exterior walls due to their combination of affordability, ease of installation, and effective thermal resistance. These batts consist of fine glass fibers and are manufactured in pre-cut panels that can fit easily between wall studs, offering a uniform insulation layer. This makes them particularly popular in both new construction and retrofitting existing walls.

Fiberglass insulation also has a good R-value, which measures the insulation's ability to resist heat flow; the higher the R-value, the better the insulation performance. Additionally, it is lightweight, non-flammable, and does not absorb moisture, which helps prevent issues related to mold and mildew within the wall assembly.

While other types of insulation, such as cellulose, spray foam, and mineral wool, have their own advantages, they tend to be used in more specialized applications. Cellulose is often chosen for its eco-friendliness and sound absorption properties. Spray foam insulation provides excellent air sealing and higher R-values but requires more labor and a professional installer for application. Mineral wool is valued for its fire resistance and soundproofing qualities but can be more expensive and less commonly used than fiberglass batts in standard wall assemblies. Thus, fiberglass batts remain the go-to choice