The Seac F1S White Fin is a modern lightweight dual material fin with a good effort:performance ratio. The combination of soft and hard materials channel water to the tip of the fin for an efficient up and down kick. Bungee Heel: The fin strap is a water resistant bungee strap that applies a constant grip on your foot as your boot compresses with depth. Bungee straps also make it much easier to don and doff your fins without having to adjust buckles and straps every time.