10x10 matting. Opening is cut to 3.5"x5.5" to securely hold a 4"x6" photograph or art print in a 10x10 inch frame (frame not included). The matboard has a bright white core. Cut with a 45 degree bevel. 4 ply/.055" thick. Acid free and PH neutral. Colors are matched as close as possible but can vary depending on each person's screen settings. Matting gives your framed photos a professional look and also protects them from damage by keeping it from making contact with the glass where moisture would get trapped and warp/discolor your photo.