The only reason I wash pre-cuts is because of the chemicals effect my fingers. So I use a small amount of Woolite or Dawn dish soap in my large salad spinner. Make sure it is well rinsed, spin, hang dry. I haven't worried about shrinkage, just the chemicals. If it's a small project that I won't be working for days on it - such as a Christmas stocking size or a small table runner, I don't pre-wash, I just wash my hands after sewing.