The tip opening of the mouthpiece can be opened or closed to change the sound or playability of the piece to the customer’s specifications. The amount that the tip opening can be altered will be determined based on the original facing of the mouthpiece, as well as the material of which it is made.  Hard rubber is the softest material and is therefore the easiest to work with.  This allows for much greater flexibility in terms of how much the tip opening can be altered when compared with harder materials such as brass, bronze and stainless steel.