Mat Board Center Premier Acid-Free Pre-Cut 8x10 Black Picture Mat Set. Includes a Pack of 25 White Core Bevel Cut Mattes for 5x7 Photos, Pack of 25 Backers & Clear Bags Set of 25 pieces of 8x10 Picture Mattes for 5x7 Photos with 25 backing boards and 25 crystal clear sleeve folding flap bags. The Mat opening size is 4.5"x6.5" for 5x7 photo prints. Color: Black. The mats are beveled cut with white core and 4-ply thick (about 1.4 mm or 1/16 inch). The backing is white on both sides. The re-sealable adhesive strip of the clear bag is below the opening of the bag instead of on the flap.