RC stands for Resin Coated, which refers to the base material. That makes it plastic, basically.
I do not write with ink on any print, so cannot comment on that specifically. My writing is done with pencil only. Pencil does not work well on the plastic base, though.
Perhaps there is a different solution? I would imagine it matters what type of ink is used, whether it will even stick to the plastic base or not.
The emulsions are similar to those in fiber paper.