The basic raw materials for producing glass fiber are quartz sand, wax stone, limestone and dolomite. In order to melt the above substances, boric acid and fluorite are added as fluxes. According to the content of Na2O, glass fiber can be divided into three categories: alkali-free glass fiber, medium alkali glass fiber and high alkali glass fiber. The alkali-free glass fiber contains 55-57% of silica, 10- 17% of alumina, 12-25% of calcium oxide, 0-8% of magnesium oxide, 8.5% of boron oxide and 0.5% of sodium oxide. Other components are the same, but the content is slightly changed.