Kim
Betty Cotton uses the 80- 20 batting because the 20% poly helps keep the top and bottom pieces sandwiched together when ironed before stitching them. Makes it easier to handle when working with the top, batting and the bottom pieces all at one time. The iron melts the poly just enough to keep them together while they are being handled. It looks good when finished. Her book is really good with the directions too. Hope this helps explain why she uses that batting. I've done a few of her projects in her book and also took her class at Sewing with Nancy. Lot's of fun.
Suzy