I'm surprised that some have never heard a felt keybushing squeak. It is somewhat rare but does happen occasionally, usually on older pianos, and usually at the balance rail pin.
Quite right, Ryan. I never gave it much thought but I only experienced balance rail bushing squeaks on American pianos. Same with whistling centres on upright butt flanges. I don't recall dealing with squeaking bushing cloth since I have been back in Europe.
I suspect graphite impregnated cloth. I seem to remember something about that in old advertising literature. As we know, graphite will make the squeak worse, given time and circumstances.
I noticed how graphite on leather or cloth can make squeaks, parafin also.
Here the keyboard pins are often lubed with cork grease, unless the bushings are in leather.
This have to be cleaned (with gasoil) and renewed from time to time, but I suppose that no squeaks can occur then.
Center bushings on Renner actions are graphited, indeed it is possible to hear a squak from a center occasionally, onlmy when the cloth is old and dry (and probably when the surface of the pin is not as neat as it should be)
Graphite is probably alittle abrasive in regard of the surface treatment of the cloth, but Renner seem to consider that the advantages are better than the inconvenience, they say (I heard of) a better reaction to humidity change, a better reaction to alcohol/water treatment.
The strips of bushing cloths I use on flanges when I change them are pre glued and graphited (and easy to use, once glued the fit for a 1275 or 1300 center is easy to obtain)
The Renner center cloth is pure wool (may be the cloth for mortises is a different quality with some cotton for instance)
I have seen extraordinary old american bushing cloth that was very springy and did not wear at all after 80 years.
Some older German/EUropean qualities where also excellent. We ironed the cloth before using in when I was younger. mortise cloth could stand for 20 years of dayly use, now it is more difficult to find a cloth that last enough.
The original "Kasimir" quality production was stopped , for environmental reasons I was said.
The red trousers of the military men under Napoleon where done with that fabrics :
Created in 1474 the name was given by the first producer of that fabrics. English name "cashmere" not to be confused with cashmere wool. English cashmeres where reputed but later France produced very good or better ones.
Seem to be only wool, originally anyway.
WIdely used for trousers.