Vent filter material in electric motors and components?

[Drewpy Dawg]

When rebuilding electrical components like distributors, wiper motors, crank angle sensors, etc. there is usually a little vent in the housing that is stuffed with a fibrous/sponge-like filter material. Presumably this is to allow hot gases to escape the housing but keep debris from getting in. Does anybody know exactly what this stuff is called or what to use to replace it? I've had situations where it is either missing or is soaked in oil but I'm not sure what to replace it with.