I agree, use the insulation. It's important that you be able to pin to whatever your design wall is made of...maybe not for all projects, but you'll really miss it if you need to pin and you can't.
Another excellent option, since you're still at the building stage, is to put up homosote, either over or instead of, drywall. You could then just hang or permanently adhere your batting/flannel/felt to the homosote, depending on how you want to impact the resale value of the house. Homosote would be more sturdy than foam insulation, yet just as easy to use.
Last edited by ghostrider; 04-06-2014 at 07:32 AM.