It's open on all four sides for superior air circulation and unrestricted venting that can help remove humidity and warmth buildup. It is a lot a lot easier and cheaper to set up a roll of Prodex than the usual cumbersome 6 inch roll of fiberglass. Pinching six inches fiberglass https://www.google.sm/url?q=https://www.advancedroofing.biz/services/commercial-roofing/