Blade material: double polymer-free technology material with high performance and high impact resistance even at low temperatures Sling belt system Rib guards to ensure longer life. Anti-slip system carefully designed to work in all positions. The f1s seam white fin is a modern, lightweight dual-material fin with a good effort:performance ratio. The combination of soft and hard materials channels water to the tip of the fin for efficient kicking up and down. Bungee heel: The fin strap is a water-resistant elastic strap that applies a constant grip on the foot as the boot compresses with depth. The elastic straps also make it much easier to take the fins on and off without having to adjust the buckles and straps each time.