Synthetic, or Flue Gas Desulphurization (FGD) gypsum, is a byproduct of coalfired power plants 3. Gypsum board is an energy intensive product to manufacture. According to an Industry Average EPD, every 93 board meters (1,000 board feet) of drywall produced requires about 5,048 MJ of nonrenewable primary energy (electricity and natural gas ...