Maximum recommended supply velocity is a critical parameter in flexible duct design as it ensures that the duct system operates within a safe and efficient range. Excessive velocities can lead to noise, vibration, and increased pressure drop, while velocities that are too low may result in inadequate airflow and system performance. The Flexible Duct Calculator provides a table of maximum recommended supply velocities for main and branch ducts, helping designers and engineers to ensure that their duct systems are designed for optimal performance and efficiency.