Johns Manville , a market-leading manufacturer of glass fiber products and Berkshire Hathaway company, has announced it will expand its glass fiber operations plant in Etowah, Tenn., to service the increasing needs of the engineered thermoplastics industry. Johns Manville, a market-leading manufacturer of glass fiber products and Berkshire Hathaway company, is expanding its glass fiber operations plant in Etowah, Tenn., to service the increasing needs of the engineered thermoplastics industry.