17x20 Matting for Picture Frame Dark Blue with Cream Core and 13x16 Opening Size (B334MAT) MAT SIZE: This matting fits a 17x20 frame. (frame not included) OPENING SIZE: This mat fits a 13x16 photo / print. (Actual opening size is 12.5x15.5) Matting Material is Crescent Mat Board. Dark Bottle Blue Finish / Cream Core with White Backing (PH Neutral). This listing includes (1) Custom Cut Mat. (The size selected represents the OUTSIDE dimensions of the matting.)