I've made lots of raggy quilts, I often use a mixture of regular cottons, flannels, corduroy, Denim.... They all work. I sometimes add a layer of inexpensive cotton muslin to the regular cotton blocks-- the muslin seems to add just enough to get the raggy edges nice like flannels. I also use cotton batting in my raggy quilts. Clip closer & shorter than with heavier ( flannel, Denim) so your edges will be like a nice chiennelle.