This is a wood and fiberglass mute for large tubas made by Ion Balu (yawn ball-oo). It features nine foam blocks in three sizes that attach with Velcro-style material. This way you can ensure a custom fit for your tuba.
This XL model fits tubas much larger than average. I tried to fit this in a Miraphone 191 and the XL mute is too large. I think the 191 and most large tubas prefer the L size. This Balu XL size mute fits better in a MW Fafner, or 6/4 York-style tuba.
Available in several colors. I usually stock the amber, which matches the inside of Disney Hall in DTLA.