Single Mat You will receive one single mat. Acid Free, White Core 4-Ply Mats Overall Size 28" x 40" - Bevel Cut Opening Size of 23.5" x 35.5" for 24" x 36" Photo Backing and Clear Bags are NOT included with this option. Our Acid-Free matboards are 4-ply and feature a White Core. With an overall size of 16" x 20", these mats fit perfectly into 16" x 20" frames. Each mat is bevel cut to enhance your 12" x 18" photos. The actual mat opening size is 11.5" x 17.5" inches so that it may safely and securely display your 12" x 18" photo, artwork, needlepoint, sign, etc.