text: 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.\n\nIt'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).