Inovart Picture-It White Pre-Cut Art/Presentation 9" X 12" Mat Frames Paperboard surface is neutral PH. Smooth, non - glare finish Mats can be decorated with oil and water - based artist paints, mediums, inks, watercolors, markers, pencisl crayon etc Board thickness is 18 ply Mats have straight cut, non - beveled edges Outside Mat Size : 12" x 16" and Art Size : 9" x 12", The (inside) frame cut-out is slightly smaller than 9"x12" as it is designed to accommodate a 9"x12" image" - the opening measures 8"x11"