Bass Trombone Cup Mutes are made of spun aluminum, and have been tested to perform evenly in all registers—creating an exciting tonal quality that results in near-perfect intonation. Jo-Ral mutes also feature neoprene-enhanced composite cork pads that provide extra durability. The result is a more pliable cork that grips well and doesn’t dry out, become brittle or break off—so it lasts longer while easily accommodating fine adjustments for a perfect fit.