Its main components are silicon dioxide, aluminum oxide, calcium oxide, boron oxide, magnesium oxide, sodium oxide, etc. According to the alkali content in the glass, it can be divided into alkali free glass fibers (sodium oxide 0-2%, belonging to aluminum boron silicate glass), medium alkali glass fibers (sodium oxide 8-12%, belonging to boron or boron free sodium calcium silicate glass), and high alkali glass fibers (sodium oxide over 13%, belonging to sodium calcium silicate glass).