Each set includes a bevel-cut white mat with a white core and a white backing board. The mat is 4-ply thick (about 1.4 mm or 1/16"). The 16" x 20" mat opening size is 10.5" x 13.5" for an 11" x 14" print. The 11" x 14" mat opening size is 7.5" x 9.5" for an 8" x 10" print.