Yes, I usually use poly batting. If the quilt is a very special one I use cotton. Most of mine are for grandchildren's use and the poly washes easily and the cost is less. I do want them to be used.

I use batting as in regular quilting

ok Thank you, I am new to quilting but have pieced tops ever since I was 12.

Bed sheets sounds like a good idea for lots of people. Like I always say if it works, do it.

I do use some batting between my quilt top and sheet. If you have some flannel fabric you could use that, you would just need to be sure to wash it first to get shrinkage out.

yes I use batting or flannel depending on what I am doing

Interesting question.

Yes, for a traditional definition of a quilt, the finished project has to have 3 layers, the top, the back, and a layer in between, usually something for warmth like cotton or other batting or wadding or old blankets or other filler. Can be thick or thin.

If the finished project has only the topping and the back, it really is more of a lined tablecloth or lined bed coverlet, more useful for beauty than warmth.