Our acid-free Brick Red matboards are 4-ply and feature a white core. With an overall size of 16x20, these mats with Oval openings fit perfectly into 16x20 frames and are bevel cut to showcase your 13x18 photos. Actual mat opening size is 12.5x17.5 inches so that it may safely and securely house your 13x18 photo, artwork, needlepoint, sign, etc. This pack includes 25 Matboard Show Kits With Acid Free Backings & Clear Bags. Proudly made in the USA by Country Art House!