Acidic insulating refractory bricks were prepared by mixing kaolin and grog with polystyrene (PS) beads up to 1.5% and bagasse up to 5% (by weight). This latter is a fibrous waste residue from the sugar cane industry. The bricks were dried and fired at 1250°C in a cycle lasting for 16 hours. The bricks were tested for water absorption, porosity, bulk density, cold crushing strength and thermal conductivity at three different temperatures (400, 600, and 800°C). It was concluded that bricks containing 1% PS and 3% bagasse abided by ASTM C155‐97 for C‐30 type insulating refractories with a bulk density of 1.01 g/cm3, a cold crushing strength of 4.08 MPa, and a thermal conductivity of 0.37 W/K/m at 800°C.