Ok so after some Google-Fu it seems as though they are plastic coated paper. I say this in part because they do seem to have a 100% plastic deck and they are clearly marked as such:
I have got these. Paper cards. Well Piatnik makes paper cards that are actually mix of paper and silk. One line is 60/40 the other are 80/20 mix. These are 80/20...very pretty but not long lasting.
I think I still have a catalogue for Piatnik and will confirm although all of their plastic cards will state plastic on the box so these would be paper.
I happen to be in Austria for work this week and can confirm that the plastic cards state that they are 100% plastic. (Spent some time in a store dedicated to playing cards and nothing else...it was very cool)