Our Acid-Free matboards are 4-ply and feature a White Core. With an overall size of 8.5" x 11", these mats fit perfectly into 8.5" x 11" frames. Each mat is bevel cut to enhance your 5.5" x 8.5" photos. The actual mat opening size is 5" x 8" inches so that it may safely and securely display your 5.5" x 8.5" photo, artwork, needlepoint, sign, etc.