ABSTRACTAn investigation of eleven types of insulating brick was made. Physical properties determined included bulk density, porosity, transverse and crushing strength, pyrometric cone equivalent, volume shrinkage at 2300°F, 2500°F, and 2700°F, load deformation at elevated temperatures, and resistance to spalling. A study of the relation between permeability and pressure differential through the various insulating brick is included in the report.Suggestions for classifying the various types of insulating brick into groups and a critical discussion of formulas for permeability are also giv