Our acid-free Oyster Shell White matboards are 4-ply and feature a white core. With an overall size of 22x22, these mats with Square openings fit perfectly into 22x22 frames and are bevel cut to showcase your 18x18 photos. Actual mat opening size is 17.5x17.5 inches so that it may safely and securely house your 18x18 photo, artwork, needlepoint, sign, etc. This pack includes 1 Single Matboard. Proudly made in the USA by Country Art House!