I don't usually prewash. However if some of it is already pre-washed, you will want to keep it consistent.
I usually only prewash my flannels.

The only time I prwash is when I am working with flannel. I have never had a problem with fabric from my lqs or with the places that I order from.

I agree, it is better to prewash it all, or none :D:D:D

If you start out cutting from prewashed fabric you should
make sure all of your fabric is prewashed. Likewise if you start out cutting with unwashed fabric you should continue with unwashed fabric. In other words do not mix prewashed with unwashed fabrics.

I would wash the new fabric.

Thanks for your post. It was very informative. I admit I was leaning towards not prewashing, but you have made such valid points that I will now. I hope your eyes get better. I suffer from allergies, and in the fall my eyes were giving me fits, too.

I wondered about jelly rolls! I guess the rule of thumb is, wash if you can. It just bothers me when I see how the cut edges fray and you lose precious fabric. You have a beautiful quilt in your avatar picture. I have some hand-dyed fabric I have been buying every year at the International Quilt Festival in Chicago every year, and I would like to eventually make a quilt like yours. So far I don't feel confident enough to attempt it.

I was recently told, by a quilting instructor that fabrics today are not "cured" for more than an hour (at one time it was 2 days) so that all cottons should be pre-washed to be sure of no surprises in your finished quilt. So, now I do, and I have found that if you get the fabric right out of the drier before it is totally dry, and smooth it out, there is very little ironing required,

I prewash all of my fabric. A bleed will break your heart!

Same here, I DO pre-wash flannels because they have a tendency to shrink but otherwise....only wash completed quilts with a color catcher