Subsequently, Penwyllt also supported the Penwyllt Dinas Silica Brick company, which quarried silica sand at Pwll Byfre from which it manufactured refractory bricks, a form of fire brick, at the Penwyllt brick works (closed 1937 or 1939). The bricks were destined for use in industrial furnaces. A narrow-gauge railway, with a rope worked incline, transported silica sand and stones to the brickworks, which was adjacent to the Neath and Brecon Railway (which on 1 July 1922 became part of the Great Western Railway).