Is this stuff downproof? What is a good synthetic fill if not. I prefer down if possible but it is more cost I think. I am no avid seamstress by far and I know synthetic is easier to work with. I really want to make a top/ underquilt. I wanted to sew some corner and side tabs to attach shock cord to for underquilt use. Any suggestions would be super. I have been checking out the many top/underquilt posts here on HF.