Spirit River UV2 Schlappen -Spirit River has used a double dye process in the production of all of the UV2 line of fly tying materials. With this special treatment, all of the UV2 material has added UV Florescence and UV Reflectance wave lengths. These fine details are sometimes so small that humans are unable to detect or perceive the difference, but they attract the fish that you are going after and need to catch. UV2 TechnologyUV FlorescenceUV ReflectanceDouble dye process