I really think if it was sold as 100% cotton, it should not be that stiff. I would try taking it back see what they say. Even though it has been washed, they may let you exchange it or something.

I've ended some extra wide fabric that was 100% cotton, and I think it was sold more as drapery liner or as an under fabric for upholstery. I used some for the curtains I just made for DH. They are pieced and quilted, but not intended to ever be used as blankets so stiff is fine.

I feel your pain. I bought some 'stiff" fabric and washed it. It helped just a little but you cannot tell it has been washed. Hopefully a second washing will help you.

I know for a fact that washing with vinegar will soften things that are very stiff up nicely. And the vinegar does not effect the fabric or the color.

It it's cotton fabric for quilting then vinegar will soften it. I have had some stiff quilt back fabric before. I sprayed it with vinegar until wet and then washed it in hot water and detergent.

That was my first thought, to wash with vinegar.

I have had two from the same seller arriver very stiff. Neither was a white on white and neither softened with washing. The orange one does seem to be softening a little as it's handled being quilted, but the blue one never did.
What did I do? Used them and upped my price on the next mail order backing.

I was wondering about that.

I would like to see picture of the curtains you made . Also did you just do a casing for the top?

Janey - Neat people never make the exciting discoveries I do.

Janey, I bound them like any other quilt. The curtain rods have rings with clips, and those clip on the binding to hold it up. I hang all my quilts the same way. They are much more like "wall hangings" than what you'd think of as "curtains" .