Manufacturer's description:
"Made of high quality hand-spun aluminum and finished with a copper bottom, the Jo-Ral non-transposing straight mute has been tested to perform evenly in all registers, and produces a powerfully dark and rich sound. The mute also features neoprene-enhanced composite cork pads that grip well and don’t dry out, become brittle or break off, and so last longer while easily accommodating fine adjustments for a perfect fit."