PUL is polyurethane laminated fabric- it is easy to work with and makes great waterproof diaper covers. I made diapers and covers for my first grandbaby a few years ago. There are many free patterns on the internet- here are a few.
http://handmadebyrita.blogspot.com/2007/10/httpwww.html
http://www.chloetoesboutique.com/store/WsPages.asp?ID=2
http://www.diapersewing.com/cover_with_snaps.htm