YES. Flexible ductwork can restrict airflow compared to metal ducts due to its design and potential for compression, kinking, or twisting. One source indicates a 12% reduction in CFM for flex duct versus metal duct of the same size. To compensate, some contractors suggest increasing the diameter of flex duct by 1″ to match the CFM of metal ducts. To keep effective airflow, proper installation and ongoing maintenance are essential.