craftgrrl | cloth pads, water resistant fabric (Reply)

Ok girls, I know that this has come up a few times here, but I'm making myself cloth pads. For the people who might be about to ask why, which seems to happen whenever they're mentioned, it's healthier for me and for the environment. Think cloth diapers. Kind of the same deal. There's lots of information available on the internet, and even a diy_pads community on LJ if you want to learn more.

So anyway, I found a tutorial that I like, and I've got the flannel and the Warm & Natural cotton batting for the lining. I've got buttons and hook & loop tape for the wing closures. But what I don't have is a good water resistant fabric for the bottom layer. And I know that a lot of people have said that although it was an option, they found it unnecessary, but I'd like to have it anyway, just as a reassurance. But, I'm more of a knitter than a sewer and have only come to sewing pretty recently. I only know fabrics by what they feel like in the store and I can recognize flannel or canvas or any of the basics. But I don't know enough about what's available, or the names for things, to know what kind of fabric I should be looking for for this water resistant layer. I was thinking that it'd be similar to what an umbrella is made of, or maybe some track pants, but I don't know what that stuff is called.

I'm trying to use things that are natural and good for me like unbleached cotton and stuff, so anything water resistant that's also not bleached/dyed/treated in some way is what I'd like to find, but I'd be happy with any recommendation you might have?