When sourcing insulating bricks (IFB), the most critical factor is the Classification Temperature, which should be at least 100-200°C higher than your actual operating temperature to prevent shrinkage. You must also evaluate the Bulk Density; lower density typically means better thermal insulation but lower structural strength. Additionally, check the Cold Crushing Strength (CCS) to ensure the bricks can withstand the physical load of the furnace structure, and verify the Thermal Conductivity (W/m·k) at specific temperature gradients to calculate energy efficiency.