Fiberglass atmospheric solar storage tanks are extremely corrosion resistant and are maintenance free. They are constructed of a thick inner liner of fiberglass with an insulation layer, usually of polyurethane and a plastic outer layer. The insulation is generally installed on site although it can be purchased factory installed for some sizes. During installation, care must be taken not to over tighten fittings which can break if too much force is used. Fiberglass tanks will last from 20 to 30 years although they generally only come with a one year warranty. Although prices vary depending on the grade of the material these tanks can rival the lined steel tanks in economy.