The most serious question raised is whether glass fibers could cause cancer through inhalation, either during the manufacturing process or while working with the material. Members of the North American Insulation Manufacturers Association (NAIMA) argue this question has been answered through extensive research, and cite experts who assert you have to physically plant a lot of glass fibers into a lab rat's chest cavity to cause cancerous cell growth. Fiberglass particles that are inhaled normally are broken down safely like household dust, studies show.
The problem is getting the government to officially reclassify this material as noncancerous. Until that happens, manufacturers and others worry litigation-weary engineers and architects may shy away from specifying it.