I’ve not found a better practice mute than the Yamaha Silent Brass System. It saved my practice when living in Chicago, surrounded by neighbors. The one I have is pictured below. Below that is the new newer model, which is even lighter, has updated audio electronics, and fits in your bell for storage. Click the images to learn more or to buy one.
Yes, they’re expensive, but they’re light, relatively freeblowing compared to every other practice mute I’ve tried (lots), and you can plug in to hear yourself, and can pipe in an mp3 player or other music source so you can play along.
I often use mine even when unplugged, because it’s freeblowing and light. But with the electronics, you can do all kinds of cool stuff, especially if you plug your output into an effects pedal, or a looping pedal. Hours of fun!
If you don’t have the kind of payola you need for a Silent Brass mute, my favorite non-electronic mute is the Dennis Wick practice mute, pictured below.