[HAM] Single louver horn compartment damping material?

[David Anderson]

In some recent photos I saw, I noticed for the first time that Leslie  
used some kind of damping material on the sides of the horn  
compartment below the louvers in the single-louver cabinets like  
21Hs, 44W, and 46Ws. I've been told it was either wool batting or  
horsehair. Anyone know for sure? How thick was it?

It's completely missing from my two 44Ws. All that remains are a few  
small staples.

David A.