The marimba has wooden bars and resonators that appear similar to that of a xylophone. The sound of the marimba is quite different from the xylophone, which sounds hard and brittle in comparison. The marimba bars are very thin, and when struck by mallets they produce a very full, mellow, open and resonant tone. Due to the thinness of the bars, this instrument does not have dynamic range or penetration. Softer mallets made from either soft rubber or yarn must be used. The marimba often has four octaves, but this can be extended all the way to five octaves.