Has anyone used one fabric type on one side of a quilt and another on the back? I made up a quilt top using "regular" material and would like to use flannel on the back. Do I have to worry about the materials shrinking differently?

Not if you prewashed everything before putting it together - a lot of people wash and dry flannel twice - just to be sure

Just make sure and pre-shrink everything. Maybe even the flannel one additional time. Lots of people make rag quilts with denim and flannel and other combinations.

I've used different types of cotton as a backing. I like fleecy type cottons and flannel on the back because it makes for a cuddly quilt. I've not had any problems.

The top was not prewashed. Should I just wash the flannel once and then put them together?

I use flannel on most all my kid quilts and have never had any problems. Please make sure the colors don't run and you should have a nice soft quilt when it is finished.

I use flannel for backing all the time. Just bought a bunch more on sale the other day. I think it is great for kids quilts, makes them more snuggly.

You can still use flannel on the back, but you will want to wash and dry the flannel first. Twice. Flannel can shrink at an astonishing rate, even on the second go-around.

Are you planning to quilt rather than tie? Quilting helps keep fabrics from shrinking excessively. The quilting ties the fabrics to the batting, so that the most the fabric can shrink is how much the batting shrinks. The heavier the quilting, the less difference there is in fabric shrinkage among the fabrics used.

For best results you need to prewash the top so it will shrink whatever it is intended to. Then prewash your flannel twice. Also, is your batting polyester? It does not shrink.

You do not want to prewash a top without first basting it to a foundation fabric, even if you are handwashing; otherwise you risk a lot of distortion. It would also be a good idea to block the top, complete with foundation fabric, while it is still very damp.

If quilting and not tying, I would skip washing the top and just be sure the flannel is preshrunk. Poly batting does not shrink, so quilting fairly closely will also keep the fabrics from shinking. Most cotton battings shrink about 3%, which gives the nice crinkling effect I like.

If the quilt will be tied rather than quilted, uneven shrinkage of fabrics can become a problem. In that case I might go to the trouble of prewashing the top.