I used a sheet for the backing of my first quilt - It was for my sister's housewarming gift - she needed something for her guest room twin bed and her favorites were turtles - I bought shee set, used the flat for the back and gave her the fitted and pillow case to match - I washed the sheet first in hot water before taking to quilter - It has survived about 7 years now with coninous washings - so yes I would use for the backs for sure!!! They come in so many colors and designs it would be easy to match a quilt top. Come to think about it I have used a sheet for sashing and then used it on the back with some of the other colors from the front - worked great!!!