Damping

Dense wool turns vibration into heat instead of noise. The tangled fibres rub against one another and the energy is spent inside the felt rather than passed on to the next panel.

Unlike rubber, felt does not harden, perish or go brittle with age, and it does not creep out of a joint under steady load. A pad fitted thirty years ago is usually still doing its job.

Sitting between two parts it also takes up tolerance. A bolted joint that would start to knock as it wears stays quiet, because the felt keeps filling the gap that opens up.

The same property makes it a striking surface. Where the energy arrives as an impact rather than a vibration, felt absorbs it and softens the blow — which is why it has been the material of choice in pianos and percussion for two centuries.