craftgrrl | Silkscreening Materials

Hey y'all

I want to start doing some silkscreening and I have some organza and embroidery hoops that will work well. However, I'm not sure what to put on the screen to block out where I don't want the paint to go. I've heard that I can use Mod Podge, but that it will warp and degrade after a few washings. I want my screens to last for a while and need some suggestions for a more permanent material. I live in L.A. and have access to craft stores, hardware stores, art supply stores and the like.

Thanks in advance!