The curved bow for string instruments enables string players to control the tension of the bow hair in order to play one, two, three and four strings simultaneously and to change easily among these possibilities. The high arch of the bow allows full, sustained chords to be played and there is a lever mechanism that affects the tension and release of the bow hair. The stick of the curved bow is bent upwards (convex) and forms a circle segment. Since the four strings of a string instrument are arranged on a curved bridge, the bow hairs must be loosened so that they can reach all three or four strings. Currently used bow sticks are slightly bent in the other direction (concave), that is it is only possible to play two strings at a time and, for a short time with a lot of bow pressure, three strings simultaneously.

Philippe Borer was a Swiss violinist, scholar and teacher.