Hi everyone. My soffits are built and I'm ready to run the flex duct through them. I'm running a 6 inch insulated flex duct to the front of the room for supply. I want to use 8 inch for the returns in the rear because I'll be putting two returns in. Can I use non insulated flex duct for the returns? I don't think I'll have enough room in the soffits for 8 inch insulated. I'll stuff insulation in the soffits after I run the duct. Will this work? What are the concerns? Is noise the only concern with this?