text: what are the purpose and the danger of fiberglass at home?   fiberglass is useful for a lot of different things including thermal insulation; acoustic insulation; fireproofing; reinforcement of plastics, cement, and textiles; gaskets and seals; etc.  it's danger stems from from its size, with a fiberglass filament commonly 3 microns in diameter and 20 or more microns in length. at that size it's been shown to be a potent carcinogen and causes nearly identical symptoms as that of asbestosis (a form of lung cancer).