I learned just recently that pre washing may not be such a bad idea. I made pillowcases with flange(I think that is what it is called) and I made more than a few. I popped them in the washer/drier and when it was time to iron them I noticed that the pillowcase itself was quite a bit smaller than the flange, so now it looks like it has a ruffle. Why did this happen you ask? Well it seems that the flange fabric was a blend. Not 100% cotton and it does not shrink. If i just prewashed it this wold not have happened. Thank you for your post. It was very clear and more than helpful.