i have made a couple of rag quilts (lap size) and never prewashed. going to try to do a quilt for hubby with a mixture of cotton and flannel (his old concert t-shirts) so curious how this will work out. i use flannel as the middle fabric - not quite as bulky but a very warm quilt. mother in law is going to get a rag quilt for christmas with cotton on top flannel in the middle and probably cotton on the back. let us know how yours turns out!