The present invention teaches that a tightly woven, and strong sheet of fiberglass may be saturated or impregnated with sodium silicate in order to produce a strong and fire resistant sheet. A sheet of silica fabric may be adhered to the sheet of fiberglass in order to provide additional protection from combustion. The present invention further teaches that a fire door core may be mass produced from fire resistant sheets, silica sheets, and that the core may be rated for fire safety by a rating agency, thus allowing door manufacturers to produce doors using that core without individually certifying each model of door. The impregnation may occur by spraying, by rolling or by other means, and the drying process of the sodium silicate occurs after it has been saturated into the fiberglass sheet.