I just finished a quilt that had flannel in the middle of it (really old flannel because it was thicker than what we see today) I would want to put something in the middle because it would add some body to the quilt. I think I'd be keeping my eye open for solid color flannel sheets that go on sale at the end of the season.

Thermore, a Hobbs batt, is what I've used for most of my summer quilts. It's very thin and light weight. It is a poly, not cotton.
If you want to use cotton Mountain Mist has a pretty thin cotton batt that I've also used successfully.

I made a quilt with no batting and used flannel for the backing. I will not do that again. I love the top, but wanted the quilt to be lighter weight. I thought since the back was flannel that would be enough. But I machine quilted it and the stitches do not look as good. When there is batting, the stitches are imbedded somewhat for a much better look. I think if you use poly or wool batting instead of cotton you will get a lighter quilt.

I've tried using just a top & bottom & then used decorative stitches to "quilt" it. top was pretty but wished I had used a muslin back instead of flannel.

I have 2 summer quilts I bought at a yardsale. They are just the top and muslim backing, I love them. One is tied and one it straight line quilted.

My M-I-L does a quilt as you go where you are sewing your pattern right onto the backing as you piece your quilt - thus the back is in place when you are done. I have never made one, but have seen hers and they are quite nice when finished; not much work to them either.

I used to make quilts for premies, and the batting would make the quilt too thick for small babies. What I discovered worked was woven blankets. I would purchase full sized blankets at a local thrift store, take them home and wash them in hot water and arm and hammer detergeant. Then I would cut the blanket to be my "batting" between the layers of the quilt. When the quilt was finished, I would wash the entire thing again in pure baking soda and dry it with no dryer sheets and seal it in gallon zipper bags to be mailed to hospital NICU's.

OK, i did this one without batting. the only problem with it was my quilting in the border doesn't really show well at all without some batting in between.
now I also made a summer reversible quilt. just simple quilt and simple quilting. no batting.

I have made a summer quilt without batting. I think next time I would use a piece of flannel as batting.

I use old flannel sheets for this.