I just made my first "summer" quilt -- for me! -- and I used flannel. I'm delighted with the weight of this quilt!
That said, last summer I used my quilt with the Hobbs wool batting for most of the summer. It was much less 'sweaty hot' than polyester is and much less dense/weighty than cotton is. It's still my all time personal favorite quilt, all season.
Jan in VA