Our Acid-Free matboards are 4-ply and feature a White Core. With an overall size of 11" x 17", these mats fit perfectly into 11" x 17" frames. Each mat is bevel cut to enhance your 8.5" x 11" photos. The actual mat opening size is 8" x 10.5" inches so that it may safely and securely display your 8.5" x 11" photo, artwork, needlepoint, sign, etc.