Actually, as Poppi pointed out, they DO need to be thin. What I found is that if the layer is thin enough, UV Mapper will map it as a single part, whereas if it's thicker, you get the separate front/back pieces, which make it impossible to create a working transmapping because the two sides won't match up and you get the problem I had, where one side is transparent and the other isn't, got it? I guess this is one of those things you learn from expirience, 'cause I've certainly never read it anywhere. Someone should write a book of little-known, off-beat facts like this, as well as hidden stuff like Poser's "Hair" feature where you type in "hair" and an undocumented window pops up, or the "secret" export feature in Bryce involving the edit pop-up (I don't remember the full procedure at the moment). In fact, I have the Real World Bryce 4 book, which has about 1,385,985.7 pages, and I don't think the export trick is even in there!