I bought 10 yds of flannel batik from SewBatik. I called them and asked if the fabric needed to be prewashed. They yes, absolutely. So, I cut it, washed it with tiny bit of detergent and Retayne in warm water on delicate cycle w/cold rinse. Also put in a dye magnet. I had cut them longer than what I needed. The colors are still beautiful and vibrant. The dye magnet turned just a very light pink. The pieces did shrink about 2 inches. So glad I cut longer than needed and am so glad I pre-washed.