Complex sentence: The major global industrial-scale use of boron compounds (about 46% of end-use) is in production of glass fiber for boron-containing insulating and structural fiberglasses, especially in Asia.
Split into simpler sentences: The major global industrial-scale use of boron compounds is in production of boron-containing fiberglasses. About 46% of global use is for boron containing glass fiber used in many types of insulating and structural fiberglasses, especially in Asia.