muslin
I am very careful anymore about the muslin I buy. No more pre-wrapped sale bolts from Joann's. That stuff had so much sizing/glue on it I had to wash on hot 3x before it softened, and you could feel the goo on it once it was wet. Ick. Only brand-name yardage that I can feel before buying, and then I usually have to hot water wash 2x to adequately remove sizing and shrink it. Best muslin comes from real quilt shops...I've had no problem at all with that kind. For the amount of effort and time pretreating takes, I'm only using the better stuff from the shops on my labor-intensive quilts. You can find reasonable stuff at chain stores, but check the end of the bolt and see it actually has a real manufacturer's label on it. If so, it's probably ok. If not, run. Bleached vs. unbleached has not been an issue if I am careful about the source. Some of my wallhangings don't really need the best quality, so then I'll get it from a chain store, but only if I can actually feel it first. Hope this helps.