I use Stable Stuff for most all my paper piecing now from the first time I tried it, it's great. but it doesn't wash away.
....If you wet or wash your finished project, Stable Stuff® Poly becomes a fine,soft layer of unnoticeable polyester fibers inside your project.
I've tried to find it in bulk from a warehouse but haven't had any luck so far. Next time I'm in Paducah for the quilt show I'm taking a piece to compare at the stabilizer booth. Every type you can imagine is there but labeled what it's made from not the brand name. It's not too bad a price though 50 pre cut sheets for $10.