My daughter made a beautiful T-shirt quilt for a friend and I took it to my quilt group for show-and-tell. She and my SIL smoke and I didn't think to take it out of the bag and look at it. When I took it out at the quilt group it reeked of smoke! I remembered that my Mom used to air the winter things that were put away with moth balls in the fall. So I took it home and hung it on a line outside on the covered patio and left it there for 24 hours. Worked great and all the odor was gone. I think I would be cautious about washing it if you don't know whether the flannel was prewashed or not. Just a thought.