Typically, for a wallhanging, you don't want old-fashioned 100% cotton batting that "crinkles" after it's washed.
Polyester battings come in different lofts. If you are machine quilting, poly batting gives a highly defined stitching line. High lofts are harder to both machine and hand quilts, so most people would use a medium loft poly if they want a "puffy" wallhanging; otherwise, low loft poly.
Warm n Natural is a good, stable cotton batting for a wallhanging.