I agree with Bear about the prewashing. In addition to preshrinking, prewashing tightens up the weave of the fabric (because of the shrinkage) and results in less fraying. I have read a lot of comments here about Kaufman Kona fabrics fraying a lot and I use Kona quite bit and don't experience this but I am a die hard prewasher. Other fabrics that are known for fraying quite a bit are homespuns and flannels. Again, I don't experience issues with excessive fraying on these types of fabric and I really think that is due to prewashing. JMHO.
Edited to add, since you have already started making the pillow cases and may not want to prewash at this stage you can use a clothing technique of zig zag stitching all your raw edges. This helps decrease the fray. Thankfully with pillow cases (assuming you are doing the burrito method) the cuts are large and won't be too much extra effort to zig zag your raw edges. If you have a serger you can serge the edges instead of French seaming them. But I definitely prefer doing a French seam when I make them.
Last edited by feline fanatic; 11-10-2018 at 07:29 AM.