Delrin is Acetal, it’s just a trade name.

Lots of plastics out there. Most of them will absorb moisture to some degree so could swell a small amount if moisture is present.

PTFE is too soft for some applications and will readily deform. There are several useful lubricated Nylons like Nylatron or Oilon.
My favourite though is a hard plastic with PTFE fibres in it called Ertalyte TX. It is nice to machine and has a low coefficient of friction.


https://www.theplasticshop.co.uk/ert...-rod-tube.html