Specification Brand : ArtToFrames BulletPoint1 : Mat is standard 4 ply material used in Custom Frame shops. BulletPoint2 : Made of lignin-free and pH-neutral materials. Fits into a(n) 21x21 Frame. BulletPoint3 : This mat will fit a 17x17 Photo. Actual opening size will be 16.75x16.75. BulletPoint4 : NOTE FOR ORDERS SOLD BY ArtToFrames ONLY: OPENING SIZE(s) MAY BE CHANGED BY CUSTOMER. Please include your desired opening size(s) by email, or through the contact seller link. If we do not receive a request for a custom size within 2 hours of your order it will be cut with the opening size listed above. Feel free to contact us with any questions you may have. Color : Smooth Black FinishType : Matte ItemDisplayDimensions_Height : 21 inches ItemDisplayDimensions_Length : 21 inches ItemDisplayDimensions_Width : 21 inches ItemDisplayWeight : 1 pounds ItemName : 21x21 Smooth Black / Black Custom Mat for Picture Frame with 17x17 opening size (Mat Only, Frame NOT Included) ItemPackageDimensions_Height : 21 inches ItemPackageDimensions_Length : 21 inches ItemPackageDimensions_Width : 21 inches ItemPackageQuantity : 1 ItemShape : Oblong ItemTypeKeyword : photo-mat-boards Manufacturer : ArtToFrames Material : paper ModelNumber : MAT-21-21x21-Black NumberOfItems : 1 OccasionType1 : Grandparents Day OccasionType2 : New Year OccasionType3 : Retirement PartNumber : MAT-21-21x21-Black Size : 21x21 StreetDate : 2017-03-25T00:00:01Z Style : Custom TargetAudience : Unisex Adult UnitCount : 1