Our Acid-Free matboards are 4-ply and feature a White Core. With an overall size of 7" x 7", these mats with square openings fit perfectly into 7" x 7" frames and are bevel cut to enhance your 5" x 5" photos. Actual mat opening size is 4.5" x 4.5" inches so that it may safely and securely house your 5" x 5" photo, artwork, needlepoint, sign, etc.