I have used interfacing (the lightest I can find) and I haven't had any problems with it. I am working on a string
spider web quilt right now and using it instead of paper under the strings, I hate ripping paper out. I will leave it
in the quilt. No, I didn't prewash the interfacing, as I haven't prewashed my batiks either. I will use the color
catcher when I wash it after it is quilted.