10 of 20x24 White Pre-cut Acid-free whitecore mat for 16x20 + back+bag 10 of 20x24 White Pre-cut Acid-free whitecore mat for 16x20 + back+bag This item comes with 10 single mats, 10 backing, and 10 bags. The opening size is 15.5"x19.5" for 16x20 print + backing board + clear bag The mats are beveled cut with white core and 4-ply thick (about 1.4 mm or 1/16 inch).