Our Acid-Free matboards are 4-ply and feature a Black Core. With an overall size of 5" x 7", these mats fit perfectly into 5" x 7" frames. Each mat is bevel cut to enhance your 4" x 6" photos. The actual mat opening size is 3.5" x 5.5" inches so that it may safely and securely display your 4" x 6" photo, artwork, needlepoint, sign, etc.