First of all, I've been lurking around here for a long time now. I finally registered today. Thanks for all the info I've gathered.
I'm building my second generator. I'm using 8x8 20 ga 316 plates. I keep going back to wanting a separator cell. I don't know what the the membrane material is called. So i don't know what to search for to find a vendor. I found this but they don't tell you what the material is, and won't answer my emails about cutting a custom size.

So what should I use? Where do I get it?