RUBBER, known as EBONITE, is imported from Germany and contains no plastic in it's composition. Mouthpieces with added plastic make the sound thin, bright and edgy, it has a notable lack of warmth and control. Also the pitch of a plastic mouthpiece is less stable whereas with rubber it's spot on even when you blow hard or are yourself a blow hard, ha. Rubber creates a rich warm sound that resonates freely, even with the DD baffle.  Other good qualities of rubber are that it plays well in tune and can be played in a variety of styles and dynamics.