I think you will need some kind of backing, not only to prevent sag but to prevent light bleed through the fabric. Light leaks through the sides as well as the ends of the fiber optics. I used 1" FRK faced OC 703 in my star ceiling panels, which are about 4'x 5' each. I put the foil facing the room and removed the foil in areas where i wanted first reflection absorbtion. You could probably use kraft paper glued to unfaced material as well, but you need something to cover at least part of the surface to prevent over-absorption. 2" might have been better, especially in preventing sag, but my ceiling is already very low. I used spray adhesive between the fabric and OC 703 to keep the fabric from sagging because it sagged on my first panel, despite efforts to stretch it as tight as possible.