Feel light, feel fast. Designed for everyday runs, the FuelCell Prism pairs lightweight support with propulsive cushioning to give you the confidence you need to fly. 6 mm drop: Due to variances created during the development and manufacturing processes, all references to 4 mm drop are approximate. FuelCell foam delivers a propulsive feel to help drive you forward. Medial post helps control pronation. Mesh upper for a lightweight, comfortable fit and feel.