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 our professional staff and are adjusted to produce our final, comfortable, easy-blowing mouthpieces. All of our mouthpieces are identical to exacting standards. FEEL the Comfort!