Soft Flex Sups Center Fins Material and design: PVC construction with a flexible Soft Flex profile for durable, reliable performance. Function and performance: Flexible center fins that provide responsive steering and steady handling on SUPs while maintaining long lasting use. Compatibility: Fits standard longboard fin boxes for easy installation and a secure fit. Longboard performance: Specifically designed to enhance the performance and stability of your longboard, delivering a steady, controlled ride. River running suitability: Ideal for river running with a streamlined design and flexible structure that supports smooth navigation, precise control, and maneuverability. Use scenarios: 1) River running on moving water or light whitewater with a SUP or longboard, using the flexible center fin to maintain control through turns. 2) Upgrading a longboard setup for more stable cruising and smoother glide, thanks to easy installation in standard fin boxes. 3) Training or beginner to intermediate river sessions where forgiving flex aids confident handling in varying currents.