What type of insulation method is explicitly disallowed as fire blocking?

Loose-fill insulation is explicitly disallowed as fire blocking due to its nature and installation characteristics. Fire blocking refers to the method of containing fires within specific areas to prevent them from spreading. Effective fire blocking materials need to be solid and maintain their integrity to obstruct fire movement. Loose-fill insulation, due to its loose and free-flowing nature, does not create a continuous barrier. It can easily shift, settle, or be displaced over time, compromising the fire safety measures intended by fire blocking requirements.

In contrast, spray foam insulation, fiberglass batts, and mineral wool insulation can effectively act as fire blocking materials because they can fill voids and maintain a solid barrier against fire penetration when installed correctly. These materials offer better stability and performance as a fire barrier compared to loose-fill insulation. Thus, in the context of fire safety and building code requirements, loose-fill insulation is not suitable as fire blocking.