Handmade from wooden rings with velvet ribbon.  Available in a variety of colors.
 
The purpose of the mute is twofold: to absorb some of the higher overtones, giving the tone a more mellow character and lower the pitch of low C, B, and Bb in increasing degrees.  Use of the saxophone mute tends to equalize the resistance in the instrument, and makes certain notes easier to control when playing softly.  - Larry Teal, "The Art of Saxophone Playing"