Our 4-ply matboards are Acid-Free and feature a White Core. With a 5" x 7" overall size, these mats fit perfectly into 5" x 7" frames and are bevel cut to enhance your 4" x 6" photos. Actual mat opening size is 3.5" x 5.5" inches so that the mat may safely and securely house your 4" x 6" photo, ar