Oh dear! you've already met the Quilt Police. You can use polyester for a puffier quilt. You can use cotton or cotton blend for a flatter look. There are no rules on what you should be putting in the middle for batt. Work with whatever you like the look of and is easiest for you to quilt with. Every batt usually comes with instructions for how far apart your quilting lines can be for their products, just follow their guidelines.You will find on this board that everyone has their own preferences with what fabric and batting they use.