Kelly Tuba Mouthpieces are made entirely of Lexan material. The 18, 24AW and 25 cup sizes are patterned after the Bach series, while the Kellyberg is patterned after the Conn-Helleberg series. All cup sizes are sampled by Kelly's professional staff and are adjusted to produce a final, comfortable, easy blowing mouthpiece. All of Kelly's mouthpieces are identical to exacting standards.