I'm wondering if all polyester is inherently flame retardant. My internet searching suggests as much. I'm making some decorative window curtains for a set, and the theatre requires them to be IFR. I'm trying to avoid buying a big bottle of Rosco product for such a small project, but also want to comply. I'm wondering if it's enough to simply choose any old polyester fabric from a fabric store, or if only certain kinds of polyester are IFR. Thanks!