I use plastic bags when I make HP or rebatch and the local soaping store uses a some kind of plastic to line their molds for CP. Works pretty well if you aren't concerned about wrinkle marks on the sides.
This is what I use... I attached it to the insides of my mold, and when I flip the sides down, they're nice and smooth and don't stick. I just wipe it off between uses, and I'm good to go with no leftover oil residue or scent. http://www.amazon.com/dp/B005M2D5BW/?tag=skimlinks_replacement-20
I am forcing the stress on the bags so I did a CPOP @ 170 degrees for 3 hours ( 1 hour to go) Oven then is shut down and mold is left in Oven for 24 hours
I have looked at the oven 3 times no warping of the bags at all.
So tomorrow I will see if it come out nicely.