Polyester vs. Cotton: When machine quilting, cotton batting or cotton-poly blend batting are best. Stay away from polyester; 100% Polyester batting pulls apart and stretches easily, making it difficult to machine quilt. We always buy 80% cotton 20% polyester (80/20) batting. We’ve found that we like the price, and the 20% polyester makes the batting less stiff. We have also used 100% cotton batting, but it is a little pricier and is not worth the extra money.
Loft: Stick to a low loft batting to make machine quilting easier. The batting we buy is a ¼” loft height…perfect for machine quilting.
Price: Batting can be expensive but if you watch for it to go on sale, it is reasonable. We buy our batting at Joann's (surprise, surprise). For queen size 80/20 batting, the regular price is $30. On sale for 50% off it costs only $15 (much better!).
You want your batting to be 5" bigger on all four sides of your quilt top. We buy the queen size packages so we can fit 1-2 quilts (depending on the size) per package of batting.
Hope this helped!!