batting
 

I'm pretty new to quilting - just working on my first big quilt. This is going to be for my husband's Lazy boy chair. Since he doesn't want it to be too thick (thinner = cooler to sit upon), I thought of using a cotton flannel bed sheet for the batting. Anyone used this before? Is it an okay substitute for batting? Anything to be aware of here when using this? Help?

You can use a flannel sheet as batting, but if it is new, be sure to wash it a time or two in hot water as it might shrink a lot, and you want that to occur BEFORE you quilt it! In warm weather areas, many just make the quilt with no batting at all, just a top and backing, but of course this won't give you much of any definition in your quilt stitching.

What Jeanne said in her post is correct. Wash the flannel because you don't want it to shrink. It will not have any dimension showing off the quilting. It will be flat as a pancake as we say in the states.