You have to be careful with the polyester, especially if it's fluffy. You can stitch it, but the stitching will come apart.
If you are going to use it as a charity quilt, and not something that would turn into an heirloom or whatnot......try this....Had a lady tell me this at a quilt shop.
Taking a piece of scrap fabric, preferrably a color that won't show thru the quilt, about 2 inches wide.....sew that to the batting. What you do is push the batting to where it would meet up and you would normally sew a seam. Lay the strip of fabric down and pin it in place, then sew the strip on each side.
It will hold better than just sewing the batting to itself, especially if it's puffy/fluffy. Make sense?
Anyway...that's what a lady at a quilt shop once told me. She says she does that for the charity quilts she makes for the homeless.
I will sew Warm and Natural together, using a zigzag. That works great!