I use sheets all the time, they last and hold up great as backing, the less i spend in the back is more i have for the front. And the front is seen more. Go for it. Never feel bad about what you have to use, old clothes etc. Thats the original way it was done so you are actually preserving the way quilts were made in the past, no waste, and money saved for the things you really need to spend it on. There is too much of a push from instructors etc to buy, buy buy and not every one can afford to spend those precious dollars so thinking recycle, repurpose in any area is always a wise choise. All quilts are beautiful whether made from new, or recycled. It is the creative effort you put into it and the fact that you are willing to spend your time doing it that makes the quilt worthy, not the cost. just a thought. DEB