Single mat – 1 mat over the picture

Double mat – 2 mats, one top of the other. The top mat has a slightly larger opening than the bottom mat to allow a small border of the bottom mat to show around the image. The offset dimension is what determines how much of the bottom mat will be shown. 1/4 inch is the most common. The opening in the top mat will equal the exact opening (not artwork size) in the bottom mat plus the offset on both sides. For example, if the opening on the bottom mat is 5 3/4 x 3 3/4 and 1/4 inch offset is selected the opening on the top mat will be 6 1/4 x 4 1/4 inches.

Triple mat – Just like the double mat but consists of 3 mats layered on top of each other with the opening of the bottom mat being just large enough to show the image, and the middle and top mats having larger openings so to reveal portions of the middle and bottom mats. The offset specified for the top mat will determine how much of the middle mat is visible.

The opening size of the middle and top mats will be based on the exact opening of the bottom mat, not the artwork opening. If you order a standard size mat such as 4x6 artwork 8x10 frame the exact opening can be seen when you add the mat to the shopping cart and in this case is actually 3 3/4 x 5 3/4 so that the mat overlaps a 4x6 inch print by 1/8 inch on all 4 sides. If you specify a custom mat opening then you will be providing the exact opening dimension of the mat and not the artwork size. The middle and top mats will be based on the dimensions you enter.