Made of ABS.
The Warm-Up reduces instrument output to a whisper, losing approximately -25dB to -35dB. With this high level of sound reduction, professionals have no hesitation in practicing in a hotel room during their tour, and it becomes possible to do long tones virtually silently backstage, or even gear up for that high section in the pit or on the bandstand.
With Best Brass’s unique acoustic design, the Sound Transformer “Warm-up†has superior intonation and less back pressure compared to other practice mutes. The fact that many professional players choose the Best Brass Warm-up prove its excellence.
One of the reasons that the Best Brass Warm-up is endorsed by many professionals is that it's very handy. Warm-up has the most compact size of all practice/silent mutes on the market and can be stored in most bells, so it is convenient to carry around.