Kelly Mouthpieces have a bolder sound, better feel, and offer more choices than many old-fashioned brass mouthpieces. Made of Lexan polycarbonate — the same material used to make bulletproof glass — Kelly's large shank trombone mouthpieces are virtually indestructible. These mouthpieces won't get scratched rims or dented shanks if dropped. Additionally, the the material does not conduct cold or heat like brass mouthpieces. The material's temperature-neutral characteristic makes Kelly Mouthpieces perfect for musicians who frequently play outdoors..