The opening size is 10.5"x13.5" for 11x14 print with backing board

 Our acid-free whitecore matboards are a 4-ply papermat that provide the aesthetic and design benefits of a bright white bevel., Each sheet of mat board has a richly colored front surface and  white core. It can be used for matting photos, art, and needlepoint. Also great for crafts, backboards, signs, children's projects, and school projects.