Using recruits from local dive shops, the study measured the energy cost of swimming (oxygen consumption as a function of velocity, i.e. aerobic velocity), body drag and efficiency of fins; and kick frequency, velocity, and maximum thrust in a swimming pool. Rigid and Flexible Fins Conserve the Most Energy Interestingly, both rigid (Attack) and flexible (Apollo) fins conserved the most. The maximum aerobic velocity was significantly higher for the Attack (6%) and Apollo taped fins (6%) and lower for the Compro (-10%). Scubapro Twin Jets, manufactured from the same Nature’s Wing patent as the Apollo, were stiffer but did not perform as economically as either the split or taped Apollos. In fact, the Scubapro fins (9%) had a significantly lower maximal aerobic velocity than all the others.