Our Acid-Free matboards are 4-ply and feature a White Core. With an overall size of 20" x 24", these mats fit perfectly into 20" x 24" frames. Each mat is bevel cut to enhance your 16" x 20" photos. The actual mat opening size is 15.5" x 19.5" inches so that it may safely and securely display your 16" x 20" photo, artwork, needlepoint, sign, etc.