I discovered this just a few months ago when I grabbed my batting roll to ready a quilt. I happened to have batting set aside for this quilt but wasn't enough. So I went to Joann's and bought more, thinking it was the same. I was shocked to find out it's approx. 1/2 the thickness (like 1/8" thick) of the previously bought batting. So I went back and found the thicker batting, only to find out it was $15.99 a yard whereas the thinner bat was, I think, $11.99. Thank God I had a 50% coupon. I bought what I needed for this quilt but guess future quilts will be, what I call, this summer-weight bat.
I don't care much for polyester batting because of all the tiny fibers that fly around when you start cutting it but that's my personal preference. I DO like the puffiness of poly bat -- just don't like to work with it for that one reason.