Friction loss is a critical parameter in flexible duct calculations as it directly affects the pressure drop in the duct, which in turn impacts the airflow and overall system performance. Accurate estimation of friction loss helps designers and engineers to select the right duct size, determine the required fan power, and ensure that the system operates within the desired pressure range. The Flexible Duct Calculator provides a method to calculate friction loss based on duct diameter, airflow, length, and number of bends, enabling users to optimize their duct design for minimal pressure drop and maximum efficiency.