Derailleur pulleys are either made of Delrin or Aluminum. I've even seen carbon ones which make no sense to me. What are the advantages of Delrin over Aluminum? or Aluminum over Delrin?

Aluminum seems noisier while Delrin is quieter in my experience.

Does Aluminum help shift better? I've tried googling this stuff but all I can find is debates over different pulleys (ceramic bearings, etc)

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