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So I have been curious about this for some time. I don't particularly have a preference myself, although I am experimenting with synthetics lately. There is a fine Tuba player in my area who only uses cork for his bumpers. What do you use and why?

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TheHatTuba wrote:For me, O-rings are always consistent and dont really break down or get matted down.

Depends on the material the O-rings are made of.

Natural rubber, silicone, EPDM, EPR, and EP absolutely will break down from exposure to aromatic hydrocarbons and petroleum oils. You can probably get away with them if you change your felts/bumpers fairly frequently, but there are definitely better options, e.g., Viton, Buna-N (Nitrile), fluorosilocone, all of which are highly resistant to petroleum products.

For my rotors I have found that cork is, even though it must be reneved every now and then, the most useful, silent and easy to work with. Other materials I have used as bumpers seems to make noise and make the rotor linkage bounce. Maybe I have not yet found a really good long live material. So, so far cork is good for me. But I am always interested in new stuff that may work better.

I have felts on the caps and cork inside.

What are the famous Blokewashers made from?

I think that most materials tend to break down when exposed to oils and the like. The synthetics last longer, but in my opinion, changing the felts and corks is a good reason to give your horn a good cleaning while you are at it.

Felts do expand and contract when either dry or soaked with oil or water. This will effect the overall precision of your alignment, but that difference might not effect playability that much, I just don't know. Anyone performed a test of this kind before?