1. Player comfort
2. Keep teeth from slipping
3. Reduce vibrations directly on the teeth
4. Protect the mouthpiece from teeth marks
Some cushions are made from soft plastic. Some of these include telate, an ingredient used to make the plastic soft, but in some players can cause health problems.
Other cushions are made from rubber. Those with an allergy to latex, the main component in rubber, should not use these cushions.
Mouthpiece cushions are available in different thicknesses from 0.3 to 0.8 mm. Bigger thicknesses offer more isolation from vibration for the teeth and more protection for the mouthpiece. Different materials and thicknesses can have a marked effect on how the player perceives the sound. Preferences vary from player to player.
A difference in a player's perception of his or her sound when using a mouthpiece cushion is due to the fact that, to a large degree, the vibrations reaching the player's inner ear are transmitted directly through the teeth and bone structure. Direct contact between teeth and mouthpiece maximizes this effect, though these direct vibrations are not heard by the audience.
For some players certain mouthpiece patches will not stick well onto the mouthpiece. Use of a different brand or other adhesive might solve this.
Mouthpiece cushions can also be used between the ligature and mouthpiece to prevent scratching.