10 of White 16x20 conservation archival whitecore mat,fits 8x10 +back 10 White 16x20 conservation archival whitecore mat,fits 8x10 +backing This item comes with 10 single mats and 10 backing The opening size is 7.5"x9.5" for 8x10 print The mats are beveled cut with white core and 4-ply thick (about 1.4 mm or 1/16 inch).