RIO's Mainstream bass fly lines have been developed to meet the overall needs of the average and novice fly fisher, and are designed to optimize rod performance with slightly heavier and shorter head lengths. Every Mainstream line undergoes the same rigorous production processes and quality control standards as all RIO fly lines, and is made in RIO's Idaho manufacturing facility. Each bass line is built with a warm water coating over a supple memory-free core, for the best in performance.