I wash and here is one of the reasons why. Yesterday I used a coupon to purchase 10 yds of perma press all cotton muslin, great dealas it came to $1.00 per yard, however the formaldehyde smell was so strong I had to wash before using, didn't want to since I didn't want to cut the 10 yds, but it was too much to handle later after washing and drying, but the odor just about drove me out of my sewing room.