Our Acid-Free matboards are 4-ply and feature a White Core. With an overall size of 18" x 24", these mats fit perfectly into 18" x 24" frames. Each mat is bevel cut to enhance your 13" x 19" photos. The actual mat opening size is 12.5" x 18.5" inches so that it may safely and securely display your 13" x 19" photo, artwork, needlepoint, sign, etc.