Our Acid-Free matboards are 4-ply and feature a White Core. With an overall size of 28" x 40", these mats fit perfectly into 28" x 40" frames. Each mat is bevel cut to enhance your 24" x 36" photos. The actual mat opening size is 23.5" x 35.5" inches so that it may safely and securely display your 24" x 36" photo, artwork, needlepoint, sign, etc.