What material was commonly used as insulation or fire retardant before 1977?

The correct answer is asbestos, which was widely used in building materials and insulation prior to 1977. Asbestos is a naturally occurring mineral known for its fire-resistant properties, which made it a popular choice in construction, insulation, and other applications requiring thermal protection and durability. Its fibrous structure allows it to resist high temperatures, which is why it was incorporated into various products, including insulation, roofing, and fireproofing materials.

However, due to health concerns associated with asbestos exposure, including its link to serious respiratory diseases and cancers, its use has been heavily regulated or banned in many countries since the late 1970s. This historical context is significant, as it illustrates how industry standards and health regulations have evolved over time in relation to fire safety materials.

Although other materials like fiberglass and mineral wool are currently widespread in insulation use due to their safety and effectiveness, they were not as commonly used prior to the restrictions placed on asbestos. Cellulose, typically made from paper and wood products, is also not associated with the same period of extensive use in fire retardant applications.