What material was once commonly used in household insulation but is now banned due to health hazards?

Asbestos was once widely used in household insulation due to its excellent insulating properties, fire resistance, and durability. However, over the years, extensive research revealed severe health hazards associated with asbestos exposure, including lung cancer, mesothelioma, and asbestosis. As a result of these health risks, the use of asbestos in construction and insulation has been heavily regulated or banned in many countries, including the United States.

Lead-based paint is highly regulated and banned for residential use, particularly in homes built before 1978, due to lead poisoning risks, but it is not primarily an insulation material. Mold is a common problem in properties, often due to humidity and water damage, but does not relate to materials used for insulation. Fiberglass is still commonly used as insulation today and does not carry the same health risks as asbestos. Thus, asbestos stands out as the material that was once prevalent for insulation but is now recognized as a significant health hazard and is banned in many applications.