Hi, again, Becky,
You were asking why certain kind of batting had to be used. The book I mentioned previously, Reversible Quilts by Sharon Pederson, has a section she wrote about preferred batting for these types of quilts. She prefers Hobbs Heirloom cotton and polyester which is 80% ctn., and 20% poly. She uses this kind for heavy or stiple quilting because it will stay put easier and is also has a little more bulk to it than just 100% ctn. For minimal quilting, 8-10" apart, she uses Hobbs Organic Cotton w/Scrim which is a fine layer attached to the cotton that helps it keep its shape better and has a little more bulk than just 100% ctn. She always presoaks and dries on low heat. She said she never uses 100% poly. batting because you have to baste it or it will shift in your machine while quilting and won't stay put with safety pins.
If you get on Amazon.com, you can bring up her book and it allows you to read sections of it that are really interesting and informative.
Bye, again, Norma