Aqua Lung Express ADJ Strap Heel Diving Fin Rubber side ribs channel the water down the length of the fin minimizing the spill-over effect. Features the ESBS (Ergonomic Strap and Buckle System). The protruding press ? to- release buttons can be operated easily even while wearing thick gloves. The strap, made of rubber with anti-aging compounds, has three convenient loops. This makes strap easy to tighten or pull up over the heel even with the thickest of gloves Over-sized, anti-slip rubber pads on the bottom of the fin