I always wash my flannel. It is very loosely woven and will shrink. Also, one time I thought I had bought good flannel and when I washed it I was so disappointed I never used it. (Should have taken it back but just gave it to a thrift store, someone may want to use it.) Just tell your son his next load has to wait, you won't regret making him wait an extra 60 minutes to finish his laundry.