The Lost Medium, designed by ...Lost surfboard innovator Matt Biolos, is a medium Speed Generating fin with a Ride Number of 7.3. Developed as a high performance model for light-weight surfers, this fin has an upright template paired with a refined tip to provide an extremely responsive feel. The latest in speed generating fins, the Gen Series features a V2 foil for fluidity and a unique blend of uni-directional carbon and fiberglass for a more stable flex pattern.