These footpockets are made from supple elastic rubber on the top, and rigid thermoplastic rubber on the sole.
The greater rigidity on the sole compared to other footpockets ensures 100% transfer of energy from your foot to the fin.
These footpockets are rail free, allowing the carbon blades to bend along their entire length. Cheaper plastic and fiberglass blades require footpockets with rails, which guide the weak blade and give it extra strength. But well-made carbon blades don't require rails to support them, and produce more power without them.