The diameter of the insulating gasket should be equal to the diameter of the pipe. This will prevent any repair material from accumulating in the annular space between the gasket hole and the tube hole, preventing bridges from forming.
The insulating gasket kit material should be of high insulating quality and, in addition to protecting the flange from corrosion, should also meet the pressure and temperature requirements of the system.
For best results, flange insulation kits must follow certain design criteria. Insulating gaskets shall be suitable for the intended flange rating, maximum pressure and temperature conditions of the system and working fluid.